WASHINGTON/TIJUANA, Mexico - President Donald Trump said on Monday Mexico should send Central American migrants seeking asylum in the United States back to their homelands, a day after US authorities shut the country's busiest border crossing and fired tear gas into a crowd there.

Sunday's incident happened after a group of migrants in the Mexican border city of Tijuana rushed at the border fencing.

It was the latest chapter in a saga that has pitted Trump's tough immigration line against thousands of migrants who have made their way north through Mexico from violent and impoverished Central American countries.

Tensions had been growing in Tijuana, and Trump said on Saturday the migrants would have to wait in Mexico until their individual asylum claims were resolved in the United States. That would be a significant shift in asylum policy that could keep Central Americans in Mexico for more than a year.

Trump went further on Monday, saying Mexico should send the Central Americans, mostly Hondurans, back home.

"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 USA. We will close the Border permanently if need be. Congress, fund the WALL!" Trump tweeted.

Mexican government officials had no immediate response.

Mexico has been in negotiations with the United States over a possible scheme to keep migrants in Mexico while their asylum claims are processed.

The team of Mexican President-elect Andres Manuel Lopez Obrador, who takes office on Saturday, says no deal has been agreed on the migrants. But officials are hinting they could remain.

"We should be objective, whatever happens they will stay in Mexico," said Alejandro Encinas, an incoming deputy interior minister. "Migrants have rights and we will respect them."

CRITICISM

US government agencies defended the response to Sunday's incident at the San Ysidro crossing south of San Diego. News pictures showing children fleeing tear gas prompted sharp criticism from some lawmakers and charities.

British aid group Oxfam said in a statement the use of tear gas was shameful.

"Images of barefoot children choking on tear gas thrown by US Customs and Border Patrol should shock us to our core," Vicki Gass, Oxfam America Senior Policy Advisor for Central America said.

Democrats and other critics called the use of tear gas an overreaction, and questioned the idea of keeping the migrants in Mexico to make asylum claims there.

Some rights advocates and legal experts were concerned that the Trump administration was seeking to exploit the melee.

Geoffrey Hoffman, a professor and director of the University of Houston Law Center Immigration Clinic which represents migrants applying for asylum, said the government would use it to push the argument that the migrants should remain in Mexico.

Still, Rodney Scott, chief US Border Patrol agent in San Diego, told CNN the vast majority of those assembled at the border were economic migrants who would not qualify for asylum, and said there were few women and children.

"What I saw on the border yesterday was not people walking up to Border Patrol agents and asking to claim asylum," Scott said, adding that authorities had arrested 42 people.

The US Department of Homeland Security said US Customs and Border Protection officers were struck by projectiles thrown by caravan members. US officials reopened the San Ysidro crossing after closing it for several hours.

US Republican Senator and Trump ally Lindsey Graham said the border "chaos" had to be dealt with "properly".

"Showing the American people we will take a tough line on future waves of illegal immigration helps build the necessary political support to deal fairly with the problems created in the past," Graham said in a statement.

WAITING GAME

Tijuana police chief Mario Martinez told a news conference on Monday that 194 Central Americans had been arrested in the 15 days the caravan has been in the area.

Separately, Mexico Immigration Authority Director Gerardo Garcia told television channel Televisa that 98 people were in process of deportation as of Sunday night.

The migrants have traveled through Mexico in large groups, or caravans. There are more than 7,000 at the US border in Tijuana and the city of Mexicali, with more than 800 others still moving toward the border.

Tijuana Mayor Juan Manuel Gastelum, who has said his city is facing a humanitarian crisis, told a local radio station the United States would take 2-1/2 to three months to start processing asylum requests, meaning the some 5,200 people currently packed into a shelter in the city could wait three months for their cases to be heard.

Many of those in Tijuana have said they will wait there until they can seek asylum. If they enter the United States, legally or illegally, they have a right to seek asylum.

Melkin Gonzalez, a 26-year-old Honduran man, recounting Sunday's tear gas firing, said: "I fell in dirty water when I was running (away) and I still don't have any clothes to change into. Even so, I'm not going back to Honduras, I want to go to the United States."

The US military said it had shifted about 300 service members from Texas and Arizona to California in recent days.

In a statement, US Northern Command said these forces would include military police, engineering and logistics units. It added that less than 200 troops had been sent home from the border mission, meaning that in total about 5,600 troops active-duty troops are on the border with Mexico.

US military officials have said they expected troops to be repositioned as the situation developed and changed.

Trump has said the migrants should not easily enter the country and on Monday he threatened again to shut down the US-Mexico border, which stretches for 2,000 miles (3,200 km).

US lawmakers face a deadline to approve funding for the federal government by Dec 7. Trump has threatened to shut down the government unless Congress pays for his planned border wall. 

Reuters