MATIAS ROMERO (Mexico) • The hundreds of Latin Americans in the "Way of the Cross" migrant caravan have infuriated US President Donald Trump, but they are not moving very fast - if at all - and remain far from the US border.

As Mr Trump vowed on Tuesday to send troops to secure the southern US border, the caravan was camped out for the third straight day in the town of Matias Romero, in southern Mexico, more than 3,000km from the United States.

The just over 1,000 migrants making up the caravan were planning to spend their fourth night there, sleeping in parks and sports fields with their belongings beside them in plastic bags and suitcases.

Most have been sleeping on the ground on large blankets or cardboard boxes. A few have small tents and sleeping bags.

"We just set up a little camp to feel a bit more comfortable and sleep. The next day, we're back to worrying about what will happen next," said Mr Nixon Gomez, a Honduran making the slow trek with the caravan.

The group has paused to meet Mexican immigration authorities, who have been caught on the receiving end of three straight days of Twitter diatribes from Mr Trump.

The activists organising the caravan say the Mexican government's National Migration Institute is offering to help the migrants get humanitarian visas to stay on in the country, since many are fleeing brutal gang violence in Latin America, home to the some of the highest murder rates in the world.

But the Mexican authorities are making a desperate plea as well, the activists say.

"They are saying, 'Please, spread out, we need there to be fewer of you'," an activist from the group People Without Borders (Pueblo sin Fronteras) said, speaking on condition of anonymity because he says he has received death threats for helping the migrants.

"It's because of Trump. There's a lot of pressure on Mexico. They've told us behind closed doors that if this stays as big as it is, with all the media coverage, they may take action," the activist added.

Mr Trump has threatened to axe the North American Free Trade Agreement, which he has called Mexico's "cash cow", if the Mexican government does not stop the migrants.

He has also threatened to cut foreign aid to Honduras, the country of origin of about 80 per cent of the migrants. The rest are from El Salvador, Guatemala and Nicaragua.

On Monday, Mexico said it had detained and repatriated about 400 migrants who were originally part of the caravan, which set out on March 25 from Tapachula, on the border with Guatemala.

Mexico arrested around 20 more migrants early on Tuesday in a raid in the eastern state of Veracruz, out of a group of about 250 caravan members who had decided to travel ahead by hopping a train.

The rest of the group remains in Matias Romero, enduring the scorching heat - and waiting. Adults were using the pause to wash clothes, as children played.

At one point, a crowd that gathered in the bleachers alongside a football pitch sang the Honduran national anthem, trying to keep people's spirits up. Activists gave advice through a bullhorn. "If the agreements (with the authorities) are not respected, the caravan will keep going," said one.

Activists have been organising such caravans every year around Easter for nearly a decade. The main goal is not to reach the US - though some participants have crossed the border in the past.

Rather, activists say, it is about raising awareness of the perilous journey that thousands of migrants make each year to find a safe home for their families.

The group's immediate objective is to reach the city of Puebla, in central Mexico, by today. They still do not know how they will get there.

In Puebla, they will have a four-day legal clinic with immigration law experts who will counsel individual migrants and families on what their options are for seeking asylum or refugee status, either in Mexico or the US.

The caravan will only take people to the border if they have strong claims for asylum, the activist said.

"This guy is very wrong," he said, referring to Mr Trump. "We aren't doing anything illegal."

"The people who are going all the way to the border are the ones who have the surest chance of gaining refugee status in the United States, which is a right protected under international law."

AGENCE FRANCE-PRESSE