CIUDAD HIDALGO, Mexico (AP) — Hundreds of Central American migrants waded across the Suchiate River into southern Mexico Monday in a new test of U.S. President Donald Trump’s Central America strategy to keep them away from the U.S. border.

The migrants moved off the border bridge and toward the river after Mexican officials told them they would not be granted passage through the country.

Amid shouts and even some fireworks they began wading across the shallow river.

On the Mexican side, migrants ran from side to side along the river bank, kicking up dust and looking for an opening in the ranks of National Guard troops sent to meet them.

Guardsmen scrambled too, trying to head off groups and detaining people where they could. There was pushing and shoving. Some guardsmen carried plastic riot shields hit with rocks tossed by migrants and they occasionally zipped a rock back into the crowd. Others jogged to get into position with long staffs. Still others carried assault rifles.

Many of migrants moved back to the river’s edge and a smaller number crossed back to Guatemala.

“You have two options: you go back to Guatemalan territory or you come with us,” Mexican immigration agents said to migrants who had crossed the river. They assured those who went with them that they would “regularize” their status, but few of the migrants believed them.