"The deployments were not directed at the migrants attempting entry on the USA side or at the fence line", the agency insisted.
Some of the migrants threw rocks at police officers on the U.S. side of the border, American authorities said.
"A group of approximately 100 people, including women and children, massed south of the border wall along with members of the media", he said. He said Mexico "advocates respect for migrants' human rights, security and integrity, while calling for respect for laws on both sides of the border". "We don't like that type of violence of throwing rocks".
The AP saw rocks thrown only after United States agents fired the tear gas.
Migrants, part of a caravan of thousands from Central America trying to reach the United States, return to Mexico after being hit by tear gas sprayed by U.S. Customs and Border Protection. The majority of migrants returned to Mexico.More news: Bengals fire coach Marvin Lewis after 6-10 season
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The incursion took place at a spot where there is border fencing, but it's a very old version that's relatively easy to penetrate.
AP, citing its own photographer at the scene, reported that the rocks were launched at the border agents by migrants only after they were pelted with tear gas.
Numerous migrants are waiting in Tijuana for a chance to apply for asylum in the US, but there was a backlog before the caravan's arrival and the wait is expected to be many months.
Per use of force policy, the incident will be reviewed by the Border Patrol's Office of Professional Responsibility. Others have found jobs in Mexico and tried to settle there.
An impasse with legislators over funding for his border wall project is behind a partial shutdown of USA government services which is now in its second week. Hundreds of people downwind of the gas were affected.
It comes as the U.S. federal government remains shut down as President Donald Trump and Congress argue over funding for his proposed border wall.
While Democratic leaders have thus far rejected Trump's demand for wall money, progressive advocacy groupsraised alarm in a letter last weekthat the Democrats' plan toreopen the governmentwould still provide the Department of Homeland Security (DHS)-which oversees CBP-with substantial funding to carry out the president's anti-immigrant agenda.