Washington (AFP) - President Donald Trump lashed out in fury Monday over immigration, an outburst triggered by images of a "caravan" of hundreds of Central American migrants headed toward the US border.

For the second straight day, Trump took to Twitter to attack Mexico for allowing the 1,500-strong group to march unimpeded toward the United States, their daily progress mapped out by US media.

He threatened to abrogate NAFTA -- the US-Mexico-Canada free trade pact -- while demanding Congress pass tougher immigration legislation and support his plan for a wall along the Mexican frontier.

He also declared he no longer supported a replacement for DACA, the program that had offered protection against deportation for about 700,000 undocumented immigrants, most of them Mexicans, who came to the US as children.

Since taking office more than a year ago, Trump has sought to crack down on legal and undocumented immigration, but some of his proposals have become tied up in court and Congress.

"As ridiculous as it sounds, the laws of our country do not easily allow us to send those crossing our Southern Border back where they came from. A whole big wasted procedure must take place," Trump tweeted in the evening, following similar comments in the morning and on Sunday.

"Mexico & Canada have tough immigration laws, whereas ours are an Obama joke. ACT CONGRESS."

The administration's own statistics showed that arrests of undocumented migrants soared in the first year of Trump's presidency, while illegal border crossings plummeted.

Data from Immigration and Customs Enforcement suggested, however, that processes to deport arrested illegal immigrants have become even more backed up than before.

"Honduras, Mexico and many other countries that the U.S. is very generous to, sends many of their people to our country through our WEAK IMMIGRATION POLICIES. Caravans are heading here. Must pass tough laws and build the WALL. Democrats allow open borders, drugs and crime!"

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The president has repeatedly tried to link immigration with crime but immigrant defenders say many immigrants are fleeing poverty and violence. Activists accuse authorities of rounding up longtime residents with families and jobs on minor infractions.

On Sunday he said Mexico "must stop the big drug and people flows, or I will stop their cash cow, NAFTA."

During his 2016 election campaign Trump called the North American Free Trade Agreement a disaster, and last year triggered a renegotiation of the 1994 pact which he has threatened to pull out of unless the US gets a better deal.

The next stage of those talks could take place next Sunday in Washington, after possible meetings between Mexican, Canadian and US negotiators this week in an effort to try to resolve remaining differences, sources said on Monday.

- 1,500 headed to border -

Mexican President Enrique Pena Nieto demanded that the United States respectfully pursue the continuing NAFTA trade talks, despite disagreements over immigration.

"We have been conducting serious negotiations," he said, expressing hope that "this spirit of positivity, mutual respect and cordiality" will continue, while looking for areas "that really favor the development of the three countries."

Organized each of the past five years by activists of Pueblo Sin Fronteras, or People Without Borders, the 1,500 migrants say they have fled El Salvador, Guatemala, Honduras or Nicaragua because of poverty and widespread violence from criminal gangs.

They set off on March 25 from the southern Mexican state of Chiapas for the US border, where many hope to apply for asylum.

Mexico's government "under no circumstances" promotes irregular migration, the government said in a statement late Monday.

It described the caravan as "a public demonstration that seeks to draw attention to the migratory phenomenon and the importance of respecting the rights of Central American migrants."

The Mexican statement said "it is not the responsibility of this government to exercise immigration decisions of the United States or any other nation."

On Monday, the caravan was passing through the mountainous southern Mexican state of Oaxaca.

Trump appears to have become aware of them over the weekend from a report on Fox News, which he regularly watches.

He accused the migrants of seeking to benefit from DACA, but a leader of the caravan countered that Trump is using it as an excuse to stop any deal on Deferred Action for Childhood Arrivals (DACA).

The program would provide those qualified -- as many as 1.8 million people -- a path to citizenship.