BROWNSVILLE, Texas (AP) — U.S. Homeland Security Secretary Alejandro Mayorkas said Friday that authorities faced “extremely challenging” circumstances along the border with Mexico days before pandemic-related asylum restrictions end.

A surge of Venezuelan migrants through South Texas, particularly in and around Brownsville, has occurred over the last two weeks for reasons that Mayorkas said were unclear.

Mayorkas noted that Mexico agreed this week to continue taking back Venezuelans who enter the U.S. illegally after asylum restrictions end Thursday, along with Cubans, Haitians and Nicaraguans. Migrants have been expelled from the U.S. more than 2.8 million times since March 2020 under what is known as Title 42 authority.

The secretary reaffirmed plans to finalize a new policy by Thursday that will make it extremely difficult for migrants to seek asylum if they pass through another country, like Mexico, on their way to the U.S. border.

“The situation at the border is a very serious one, a very challenging one and a very difficult one,” Mayorkas said.

Illegal crossings tumbled after President Joe Biden announced asylum restrictions in January, but they have risen since mid-April. Brandon Judd, president of the National Border Patrol Council, said this week they have been hovering around 7,200 daily, up from about 5,200 in March.

Border Patrol Chief Raul Ortiz said 1,500 active-duty troops will be dispatched to El Paso, Texas, adding to 2,500 National Guard troops already positioned across the border. Ortiz said El Paso was chosen because it has been a busy corridor for illegal crossings over the last six months. The troop deployment was announced this week but not the location.