Migrants run after U.S. Border Patrol agents throw tear gas to the Mexican side of the fence after the migrants climbed the border fence to get into the U.S. side to San Diego, from Tijuana, Mexico, Tuesday, Jan. 1, 2019. Discouraged by the long wait to apply for asylum through official ports of entry, many migrants from recent caravans are choosing to cross the U.S. border wall and hand themselves in to border patrol agents. (AP Photo/Daniel Ochoa de Olza)
camera (The Associated Press) Migrants run after U.S. Border Patrol agents throw tear gas to the Mexican side of the fence after the migrants climbed the border fence to get into the U.S. side to San Diego, from Tijuana, Mexico, Tuesday, Jan. 1, 2019. Discouraged by the long wait to apply for asylum through official ports of entry, many migrants from recent caravans are choosing to cross the U.S. border wall and hand themselves in to border patrol agents. (AP Photo/Daniel Ochoa de Olza)

Mexico's foreign affairs ministry has formally asked the United States government to conduct a thorough investigation into a Jan. 1 incident in which U.S. agents fired tear gas into Mexico to stop crossing migrants.

In a statement Thursday, the ministry said through its embassy that it lamented any violent acts along its border. It reiterated its commitment to the safety of migrants.

In the first hours of the new year, about 150 migrants attempted to breach the border fence in Tijuana. U.S. Customs and Border Protection said that agents fired gas at migrants throwing rocks. It said it was investigating.

But an Associated Press photographer at the scene only saw rocks thrown after agents fired gas as migrants scaled the fence.

The confrontation was at least the second time in a little over a month that U.S. authorities have fired tear gas into Tijuana. The action drew sharp criticism from politicians and activists on both sides of the border and raised questions about the use of force against migrants.