TIJUANA, Mexico — Mexico looked set to shore up security near its border with the United States on Monday, and local authorities said that 39 migrants were arrested after a peaceful march devolved into mayhem when U.S. agents fired tear gas into Mexico to stop some migrants who tried to breach the international line.

Mexico’s Interior Ministry said it would immediately deport those who tried to “violently” enter the U.S. from Tijuana. Meanwhile, Tijuana’s municipal government said that more than three-dozen migrants were arrested for disturbing the peace and other charges stemming from the march and what followed.

On Sunday, the situation at the border devolved after a large group marched to the U.S. border to appeal for the U.S. to speed processing of asylum claims for Central American migrants marooned in Tijuana.

There, some attempted to get through the fencing and wire separating the two countries, leading U.S. agents to fire tear gas.

American authorities also shut down the nation’s busiest border crossing at San Ysidro for several hours at the end of the Thanksgiving weekend.

Fumes Were Carried by the Wind

Lurbin Sarmiento, 26, of Copan, Honduras, said she had been with her 4-year-old daughter at a concrete riverbed, which had a trickle of water from the Tijuana River, when U.S. agents fired the gas.

“We ran, but the smoke always reached us and my daughter was choking,” Sarmiento said, visibly shaken.

She said she never would have gotten that close with her daughter if she thought there would be tear gas.

Fumes were carried by the wind toward people who were hundreds of feet away.

“We ran, but when you run the gas asphyxiates you more,” said Honduran migrant Ana Zuniga, while cradling her 3-year-old daughter Valery in her arms.

As the chaos unfolded, shoppers just yards away on the U.S. side streamed in and out of an outlet mall, which eventually closed.

Throughout the day, U.S. Customs and Border Protection helicopters flew overhead, while U.S. agents on foot watched beyond the wire fence in California.

U.S. Authorities Will Continue ‘Robust’ Presence

Department of Homeland Security Secretary Kirstjen Nielsen said in a statement that U.S. authorities will continue to have a “robust” presence along the Southwest border and that they will prosecute anyone who damages federal property or violates U.S. sovereignty.

“DHS will not tolerate this type of lawlessness and will not hesitate to shut down ports of entry for security and public safety reasons,” she said.

More than 5,000 migrants have been camped in and around a sports complex in Tijuana after making their way through Mexico in recent weeks via caravan. Many hope to apply for asylum in the U.S., but agents at the San Ysidro entry point are processing fewer than 100 asylum petitions a day.

Francisco Vega, the governor of Baja California, said almost 9,000 migrants were in the state and called it “an issue of national security.” Vega issued a public appeal to the federal government to take over responsibility for sheltering the migrants and deport those who were breaking the law.

Tijuana Mayor Juan Manuel Gastelum on Friday declared a humanitarian crisis in his border city of 1.6 million, which he says is struggling to accommodate the crush of migrants.

Irineo Mujica, who has accompanied the migrants for weeks as part of the aid group Pueblo Sin Fronteras, said the aim of Sunday’s march toward the U.S. border was to make the migrants’ plight more visible to the governments of Mexico and the U.S.

Trump Repeatedly Suggests Migrant Caravans Are Full of Criminals

“We can’t have all these people here,” Mujica said.

On Monday, U.S. President Donald Trump took to Twitter to express his displeasure with the caravans in Mexico and to make another pitch for his promised border wall.

Mexico should move the flag waving Migrants, many of whom are stone cold criminals, back to their countries. Do it by plane, do it by bus, do it anyway you want, but they are NOT coming into the U.S.A. We will close the Border permanently if need be. Congress, fund the WALL!

— Donald J. Trump (@realDonaldTrump) November 26, 2018

“Mexico should move the flag waving Migrants, many of whom are stone cold criminals, back to their countries,” Trump tweeted. “Do it by plane, do it by bus, do it anyway you want, but they are NOT coming into the U.S.A. We will close the Border permanently if need be. Congress, fund the WALL!”

Trump has repeatedly suggested without evidence that the migrant caravans are full of hardened criminals, but they are mostly poor people with few belongings who are fleeing gang violence. During his presidential campaign, he promised he’d have Mexico pay for a wall.

Mexico’s Interior Ministry said Sunday the country has sent 11,000 Central Americans back to their countries of origin since Oct. 19, when the first caravan entered the country. It said that 1,906 of those who have returned were members of the recent caravans.

Mexico is on track to send a total of around 100,000 Central Americans back home by the end of this year.