Mexico is bracing for the possible arrival of the "mother of all caravans," officials warn.

Interior Secretary Olga Sanchez Cordero has said a caravan of migrants from El Salvador, Honduras and Guatemala could be forming — and it's huge.

"We have information that a new caravan is forming in Honduras, that they're calling 'the mother of all caravans,' and they are thinking it could have more than 20,000 people," Sanchez Cordero said Wednesday.

Pro illegal immigrant activists say that's not true. Irineo Mujica, who has helped lead several caravans in Mexico, said reports about "the mother of all caravans" were false, claiming "this is information that [U.S. Homeland Security Secretary Kirstjen] Nielsen is using to create fear."

She and other pro-illegal group claim the administration of President Donald Trump may be trying to fan fears of a big caravan to turn the U.S. national agenda back to the immigration issue.

A caravan of about 2,500 Central Americans and Cubans is currently making its way through Mexico's southern state of Chiapas. The largest of last year's caravans in Mexico contained about 7,000 people at its peak, though some estimates ran as high as 10,000 at some points.

Under pressure from the Trump administration, Mexico appears to be both tiring of the caravans and eager not to anger the United States.

It has stopped granting migrants humanitarian visas at the border, and towns along the well-traveled route to Mexico City sometimes no longer allow caravans to spend the night.

Mexican President Andres Manuel Lopez Obrador said Thursday that Mexico is doing its part to fight immigrant smuggling.

"We are going to do everything we can to help. We don't in any way want a confrontation with the U.S. government," he said. "It is legitimate that they are displeased and they voice these concerns."

Sanchez Cordero has pledged to form a police line of "containment" around Mexico's narrow Tehuantepec Isthmus to stop migrants from continuing north to the U.S. border.