The Trump administration has begun an effort to send some asylum seekers encountered at the U.S.-Mexico border to Guatemala, a move that promises to transform the U.S. asylum system, according to three officials briefed on the initiative and related training materials.

The program initially will be applied at a U.S. Border Patrol station in El Paso, Texas. The first phase will target adults from Honduras and El Salvador and the aim will be to process them within 72 hours, according to the three officials and notes from a training session of U.S. Citizenship and Immigration Services (USCIS) asylum officers taken by one of the officials.

Federal immigration authorities interviewed one migrant through the new process on Tuesday and two more on Wednesday morning, the officials said. The officials did not know when the first flights to Guatemala would take place.