U.S. Border Patrol agents returned fire after shots were fired at them from Mexico along the Rio Grande in the San Elizario area southeast of El Paso, a U.S. Customs and Border Protection official said.

President Donald Trump's promises of mass deportations, which could bring batches of new arrivals fresh off the border bridges into Juárez, has Mexican law enforcement preparing to keep watch for potential trouble.

A key component of Mexico avoiding threatened Feb. 1 Trump administration tariffs on exports to the United States is that country’s ability to take back more deported migrants.

Former Border Patrol Chief Victor Manjarrez Jr. has described the tunnel as "sophisticated" and said it was likely used to "bring people from China, from Southeast Asia or Europe that can pay $25,000 to $30,000 to be smuggled to the United States."