A migrant caravan passes through Guatemala in October 2018. Another is en route through Mexico, and yet another large one believed to be forming in Honduras - REUTERS

Mexico’s interior minister has warned that “the mother of all migrant caravans” is gathering in Honduras, as President Donald Trump again threatened to seal the US-Mexican border.

Olga Sanchez-Cordero said the caravan, forming in the Central American nation, was 20,000-strong. Another caravan of roughly 2,500 migrants is currently heading north.

Mexican officials announced that the government is was seeking to set up a "containment" belt of federal forces across the Isthmus of Tehuantepec, which is the narrowest part of the country's south and the easiest to control.

The governments of Guatemala, Honduras, El Salvador and the United States on Thursday announced they had agreed to a series of measures, including joint police work, improved border security, and efforts to deter international crime and curb "irregular migration."

Mr Trump, however, insisted on Thursday that more should be done.

"May close the Southern Border!" the president tweeted.

Mexico is doing NOTHING to help stop the flow of illegal immigrants to our Country. They are all talk and no action. Likewise, Honduras, Guatemala and El Salvador have taken our money for years, and do Nothing. The Dems don’t care, such BAD laws. May close the Southern Border! — Donald J. Trump (@realDonaldTrump) March 28, 2019

"Mexico is doing NOTHING to help stop the flow of illegal immigrants to our Country. They are all talk and no action.

"Likewise, Honduras, Guatemala and El Salvador have taken our money for years, and do Nothing. The Dems don't care, such BAD laws."

The new threat to shut one of the world's busiest borders, separating two countries with massive economic and cultural links, shows Mr Trump is doubling down on his bid to make immigration a keystone of the gathering 2020 re-election campaign.

Andres Manuel Lopez Obrador, Mr Trump’s Mexican counterpart, rejected the criticism, saying on Thursday: "We are doing something on this issue."

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He added: "We are going to help in every way we can. We don't in any way want a confrontation with the United States."

Andres Manuel Lopez Obrador, president of Mexico

But Mr Lopez Obrador, who during his electoral campaign last year trod a fine line between standing up for Mexico and avoiding antagonising Mr Trump, said a solution would depend on "fundamentally addressing the causes of migration."

Kevin McAleenan, border protection agency commissioner, said on Wednesday that the southwestern frontier faces "an unprecedented humanitarian and border security crisis."

The border agency took in more than 12,000 migrants this week, it said, while just half that number would be considered already reaching "crisis level."

The agency is on track to detain more than 100,000 people in March - the highest monthly total in a decade.

Attempts to get across the border into the United States illegally are down substantially from a decade or more ago, but the last year has seen a surge.

Furthermore, the trend of arrivals has changed from single men to families and often small children - greatly complicating the task of authorities in providing basic services to detained migrants, while their cases are decided.