– Hundreds of Central American migrants waded across the Suchiate River into southern Mexico on Monday in a new test of 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 riverbank, looking for an opening in the ranks of National Guard troops sent to meet them.

Guardsmen scrambled, too, trying to head off groups 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 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.

"Mexico's president said he would give us work and an opportunity and look, "said Esther Madrid, a vendor who left her six children in Honduras. Sitting on a rock among dozens of people who didn't know what to do next, she offered only one word when asked whether she would consider returning to San Pedro Sula: "Never."

By early afternoon, the stalemate resumed, the difference being that the migrants were now on the Mexican side of the river.

Riot police with shields also appeared on the Guatemala side of river, raising questions about what options remained for the migrants.

Daisy Perez, 42, traveling with two children, used a break in the action to call a relative: "We're in Mexico, send us money."

A 14-year-old girl was carried from the riverbank unconscious. It was unclear what had happened.

The migrants want free passage across Mexico to the U.S. border and Mexico's government rejected that.

While the government says the migrants are free to enter — and could compete for jobs — in practice, it has restricted such migrants to the southernmost states while their cases are processed by a sluggish bureaucracy.

A letter relayed to the migrants on Monday by Mexico's immigration agency restated the government's position that the migrants would be allowed to enter in orderly fashion, while rejecting free passage.

Edwin Chavez, 19, of Tegucigalpa, said, "By river, that's the way it will be."

"There's no fear," Chavez said. "We're already used to repression. In your country they repress you, they hit you. It's always like that."

Earlier, a migrant stood near the shuttered gates on the bridge over the Suchiate River and read an open letter from the group to President Andres Manuel López Obrador. "We have come peacefully to try to start a dialogue with the government, in order to reach an agreement in which all the members of the caravan will be allowed permission to freely pass through Mexican territory," he read.

Trump has forced asylum-seekers to remain in Mexico, or apply in Central American countries, effectively removing one of the escape valves for previous caravans. Under threats of trade or other sanctions from the Trump administration, Mexico has stopped an earlier practice of allowing migrants to cross its territory unimpeded.

Guatemala issued new data showing that 4,000 migrants crossed into the country through the two primary crossings used by the migrants last week, and over the weekend nearly 1,700 entered Mexico at two crossings. It said 400 were deported from Guatemala.