KIEV, Ukraine (CNN) -- The missile that hit Malaysia Airlines Flight 17 most likely was fired by pro-Russian separatists inside eastern Ukraine, a preliminary classified U.S. intelligence analysis concluded, according to a U.S. defense official with direct access to the latest information. The official declined to be identified due to the sensitivity of the information. Earlier, a senior U.S. official said the United States concluded that a missile shot down the plane.
Accusations fly as investigators seek answers in MH17 crash
Ukrainian Prime Minister Arseniy Yatsenyuk on Friday blasted the "terrorists" he blamed for shooting down Malaysia Airlines Flight 17 over Ukraine a day earlier, with 298 people aboard.
He called on all governments to back the investigation and "to support the Ukrainian government to bring to justice all these bastards who committed this international crime."
Since the Malaysia Airlines jet fell from the sky above eastern Ukraine on Thursday, Russia and Ukraine -- which routinely uses the word "terrorists" to describe pro-Russian separatists -- have traded blame and accusations.
"Terrorists have killed almost 300 persons with one shot," Ukrainian President Petro Poroshenko said Thursday. "Among them are women, children, citizens of different countries of the world."
Russian President Vladimir Putin pointed the finger back at Ukraine, blaming its recent tough military operations against separatists for the volatility in the region.
But Ukrainian Foreign Minister Pavlo Klimkin rejected that claim, telling CNN it was up to Russia to stop the flow of heavy weaponry across Ukraine's eastern border and push the separatists to embrace a cease-fire.
He also dismissed any suggestion that Ukrainian forces may have been involved in Thursday's tragedy.
"There was no way our forces could be engaged in any way in this incident," Klimkin said, adding that Ukraine did not have any military assets in the area that could have shot down MH17.
Klimkin says Ukraine intercepted telephone calls between "terrorists" at the time the plane was shot down.
Yatsenyuk called for a U.N. Security Council meeting to be held and for all nations to do everything they could to stop what he said was not now just a war in Ukraine or Europe, but a "war against the world."
Meanwhile, international inspectors headed to the crash site Friday tasked with finding the plane's flight data recorders, which may lie amid the human remains and debris strewn across fields near the town of Torez.
Ukrainian government officials said 181 bodies had now been found.
German Chancellor Angela Merkel urged a cease-fire to allow a swift, independent investigation into what happened, adding that "there are many indications that it was a shot or rocket fired at the plane."
Monitors head to crash site
A helicopter ferried a group of monitors from the Organization for Security and Cooperation in Europe to rebel territory in the Donetsk region. They planned to continue by car to the crash site near Torez.
Michael Bociurkiw, who was traveling with about 30 colleagues, told CNN the OSCE had been given assurances by separatist leaders that they would be able to pass through rebel-held checkpoints.
OSCE monitors in eastern Ukraine to monitor the civil conflict have previously been taken hostage by separatist groups.
There have been conflicting reports over whether the plane's data recorders have already been recovered by rescue workers or separatists. Ukrainian officials have suggested separatists may seek to take them to Moscow.
An adviser to Ukrainian Minister of Internal Affairs Anton Heraschenko was quoted by Ukraine's Interfax news agency Friday as saying that the missile launcher used to down the Malaysian plane is already in Russia and will be destroyed.
The "BuK" launcher, as well as the flight data recorders from MH17, were handed over to Russian agents across the border at a checkpoint in the Luhansk area overnight, Heraschenko claimed, citing Ukrainian intelligence sources.
Ukraine's state security chief has also accused two Russian military intelligence officers of involvement in Thursday's events. Valentyn Nalyvaichenko said he based his allegation on intercepts of phone conversations between Russian officers, saying the conversation implicates the pro-Russian side.
CNN cannot confirm the authenticity of the recording.
Ukrainian officials reported earlier this week that two Ukrainian military aircraft had been shot down in the country's east. They accused a Russian fighter of shooting down a Ukrainian jet Wednesday and said Russian weapons had been used against an An-26 military transport plane Monday.
In an exclusive interview with the state-run Russia 24 TV channel, Russian Foreign Minister Sergey Lavrov said Russia would "insist on the most objective, most open and independent investigation" into what happened to Flight 17.
"We're ready to make our own contribution, but certainly we believe the initiative must be undertaken by the authorities of the country on which territory this tragedy occurred," he said.
"With regard to the claims raised by Kiev, that it was almost us who did it: in fact I haven't heard any truthful statements from Kiev over the past few months."
'Outrage against human decency'
If the pro-Russian separatists did shoot down Flight 17, the jet's passengers and crew are innocent casualties in Ukraine's separatist armed crisis.
The passengers and crew hailed from all over the world, including Australia, Indonesia, Malaysia, Germany and Canada. Shortly after the plane fell from the sky, international leaders scrambled to confirm how many of their citizens were aboard.
The United States has not said whether its citizens were among the passengers, but the diversity of the victims' nationalities turned the crash into a global tragedy. No survivors have been found.
Malaysian Transport Minister Liow Tiong Lai offered his condolences Friday to the families of those aboard the downed plane and said Malaysia would support them.
The full passenger list will be released once all the next-of-kin have been contacted, he said. More than half of those who lost their lives were from the Netherlands, from where the flight set off for Malaysia.
If reports that the jet was shot down are confirmed, "it would contravene international law and be an outrage against human decency," the minister said, speaking to reporters in Kuala Lumpur.
He defended the routing of the Malaysia Airlines plane over a conflict area, saying other carriers were sending their aircraft through the same airspace above Ukraine in the hours before MH17 came down.
Malaysia's transport minister said Ukraine would lead the investigation.
'Blown out of the sky'
Leaders and diplomats from around the world are pleading for investigators' access to the disputed region.
U.S. Vice President Joe Biden said Ukraine's President had accepted an offer of U.S. experts to help investigate the crash.
The plane was apparently shot down,"not an accident, blown out of the sky," Biden said Thursday.
"It is critical that there be a full, credible, and unimpeded international investigation as quickly as possible," the White House said in a statement.
On Thursday, a senior U.S. official said the United States has concluded that a missile shot down the plane but has not placed any blame.
A radar system saw a surface-to-air missile system turn on and track an aircraft right before the plane went down, the senior U.S. official said. A second system saw a heat signature at the time the airliner was hit, the official said. The United States is analyzing the trajectory of the missile to try to learn where the attack came from, the official said.
The Obama administration believes Ukraine did not have the capability in the region -- let alone the motivation -- to shoot down the plane, a U.S. official told CNN's Jake Tapper.
But the White House placed some blame on Russia and warned that evidence must not be tampered with.
"While we do not yet have all the facts, we do know that this incident occurred in the context of a crisis in Ukraine that is fueled by Russian support for the separatists, including through arms, materiel and training," it said in a statement.
But defense expert and retired Brig. Gen. Kevin Ryan said Ukraine and Russia both have the missile capability to shoot down such an aircraft at such an altitude.
Who was on the plane?
The 15 crew members on Malaysia Airlines Flight 17 were all Malaysian nationals, officials said.
Malaysia Airlines also gave a breakdown of the known nationalities of the 283 passengers: 154 were Dutch, 28 were Australian, 28 were Malaysian, 12 were Indonesian, nine were from the United Kingdom, four were from Germany, four were from Belgium, three were from the Philippines, one was Canadian and one was from Hong Kong.
But Dutch Security and Justice Minister Ivo Opstelten says there were 173 Dutch citizens aboard Flight 17.
Authorities were still trying to determine the nationalities of the other passengers.
The International AIDS Society said in a statement that "a number" of its members were on the plane on the way to a conference in Melbourne, Australia.
"At this incredibly sad and sensitive time, the IAS stands with our international family and sends condolences to the loved ones of those who have been lost to this tragedy," the statement said.
The plane was headed to the Malaysian capital of Kuala Lumpur from Amsterdam, which is a common route, CNN aviation safety consultant Mary Schiavo said. She said that the plane was flying over a troubled area and that close communication with air traffic controllers would be a key necessity.
In hostile or disputed areas, "any alteration from your course, and you can have a problem," Schiavo said.
Tensions have been high between Ukraine and Russia since street protests forced former pro-Moscow President Viktor Yanukovych from power in February. Russia subsequently annexed Ukraine's southeastern Crimea region, and a pro-Russian separatist rebellion has been raging in Ukraine's eastern Luhansk and Donetsk regions.
Ukraine's government has accused Russia of allowing weapons and military equipment, including tanks, to cross the border illegally into the hands of pro-Russian separatists.
Three months ago, the U.S. Federal Aviation Administration prohibited U.S. airlines from flying in areas some way south of where Flight 17 crashed Thursday.
"Due to the potential for conflicting air traffic control instructions from Ukrainian and Russian authorities and for the related potential misidentification of civil aircraft, United States flight operations are prohibited until further notice in the airspace over Crimea, the Black Sea and the Sea of Azov," the FAA said in April.
Various nations, including France, have ordered their airlines to avoid Ukrainian airspace until the cause of crash is known.
The Ukrainian Ministry of Infrastructure announced Friday that the airspace over the eastern Ukraine region of Donetsk, Luhansk and part of Kharkiv where separatists are operating had been closed indefinitely.
Merkel stressed Friday that Russia must do more to ease the crisis in Ukraine.
"Russia is largely responsible for what's happening in the Ukraine now, and I would make an appeal -- that the Russian President and the Russian government should make a contribution so that a political solution can be found," she said.
European Union leaders agreed this week to expand sanctions against individuals and entities in response to Russia's actions in Ukraine, with details to be decided by the end of the month. Expanded U.S. sanctions were also announced in Washington.
Thursday's crash marks the second time this year that Malaysia Airlines has faced an incident involving a downed plane.
On March 8, Malaysia Airlines Flight 370 disappeared with 239 people on board. Searchers have found no trace of the Boeing 777 or its passengers despite extensive search efforts.
Flight 370 probably flew into the southern Indian Ocean on autopilot with an unresponsive crew, Australian authorities said last month.
A new underwater search is expected to begin in August. It will be broadly in an area where planes and vessels had already looked for debris on the surface of the water.
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