According to Buzzfeed News, late Sunday evening, Border Patrol agents temporarily closed the San Ysidro Port of Entry, one of the most used border crossings in the entire world, to prevent Central American asylum seekers from getting into the United States after they had evaded Mexican police, crossed a river and went down a side street. In response to the migrants’ approach, the United States Border Patrol fired tear gas and rubber bullets while the group approached a metal fence that train tracks run through. According to a witness on the scene, at least one person made it through to the other side but was quickly detained by a border agent.

A unanimous Mexican official communicated to Buzzfeed News that Mexican law enforcement was attempting to identify those who crossed the border “violently” so that they could be deported back to Central America, where most of them are fleeing sustained threats. An hour after the initial use of tear gas, Border patrol agents also used tear gas on another group crossing the Tijuana River, making that group disperse and flee. Together, the two incidents lasted about two hours, ending in a retreat by the asylum seekers.

The marching asylum seekers were initially turned away at the border crossing by Mexican police. Little is yet known about the role in the chaotic response to migrants played by the U.S. troops stationed at the border.Previously, Trump had called for the soldiers stationed in Mexico to “shoot back” if the group threw rocks at them, prompting comparisons to Israel’s treatment of Palestinians at the border between Israel and Palestine.

An anonymous spokesperson for the US Northern Command, which oversees troops in the U.S., issued a conflicting report, telling Buzzfeed reporters that the active duty troops would not be performing any law enforcement duties, but later telling them that military engineers “moved barricades and military police as part of the additional personnel presence” at the request of the U.S. Customs and Border Protection.

The group of asylum seekers has now grown to about 5,127 people, and many of them camping inside a nearby sports complex. As the group made its way from Central America into Mexico, it had been generally well received in Mexico, but as the group reached Tijuana, which is situated in close proximity to the U.S. border, anti-immigrant sentiment began to crop up, culminating in an anti-immigrant march and indications from the Tijuanan government about “limited resources.”