Donald Trump threatened on Thursday to seal America's southern border with military force unless Mexico intervenes to stop the flow of illegal immigrants traveling to the U.S. from Central America.

The stern, tweeted warning came as a group of more than 4,000 travels north through Mexico in the hope of reaching the United States, despite having no visas or other legal papers to enter.

Trump blamed his Democratic rivals for the resulting chaos, saying 'they want Open Borders and existing weak laws.'

He resurrected the claim that launched his White House campaign in 2015, saying that 'this large flow of people' includes 'MANY CRIMINALS' and putting the words in uppercase letters for effect.

'I must, in the strongest of terms, ask Mexico to stop this onslaught – and if unable to do so I will call up the U.S. Military and CLOSE OUR SOUTHERN BORDER!' Trump wrote.

'All Democrats fault for weak laws!' he added.

President Donald Trump threatened on Thursday to use the U.S. military to close the southern border unless Mexico helps stop flow of Central American immigrants traveling from the south

Honduran migrants walked north toward the U.S. on Wednesday from Chiquimula, Guatemala, part of a massive surge that has infuriated the president to threaten financial penalties on Central American nations

The president renewed his complaint that the Guatemalan, Honduran and Salvadoran governments are doing nothing to stop a massive flow of people northward, 'INCLUDING MANY CRIMINALS'

Trump on Thursday also renewed Wednesday's threat to stop all payments to Guatemala, Honduras and El Salvador, including humanitarian aid, if their governments 'allow their citizens, or others, to journey through their borders and up to the United States.'

Secretary of State Mike Pompeo is scheduled to fly to Mexico on Friday.

News emerged Wednesday that the number of illegal immigrant families crossing the U.S.-Mexico border has jumped 80 per cent since Trump ended his 'zero tolerance' policy in June, with U.S. Border Patrol agents arresting 16,658 family members in September. That's the highest one-month total on record.

The Washington Post obtained unpublished Department of Homeland Security statistics and published them three weeks before a contentious midterm election, while Trump is urging Republicans to make immigration their number one issue on the campaign trail.

The number of immigrant families crossing into the U.S. illegally has jumped 80 per cent since Trump ended his 'zero tolerance' policy

'We're getting hammered daily,' said one Border Patrol agent in South Texas told The Post.

The new numbers also come as a wave of immigrants is on the march from Central America.

Thousands of people from Honduras, Guatemala and El Salvador are fleeing to the United States in an effort to escape the poverty and violence that has engulfed their countries.

The Department of Homeland Security, in a statement, blamed congressional inaction and said the high illegal immigrant flow would likely continue without movement on on Capitol Hill.

'Our nation faces a dangerous crisis on the border that threatens American communities. Congress refuses to close catch-and-release loopholes in the law that would allow authorities to detain and remove family units safely and expeditiously. While we do not have official numbers to report at this time, current trends indicate enforcement efforts against single adults entering illegally have been hugely successful,' said Department of Homeland Security spokesperson Katie Waldman.

'However, the removal of actual family units, or those posing as family units, has been made virtually impossible by Congressional inaction – which will most likely result in record numbers of families arriving illegally in the United States this year. At the direction of the President, DHS is continuing to examine all options to secure the border and keep American communities safe, including working with our partners in Central America and Mexico.'

The new numbers have left the president furious, White House aides told the Post.

'We're actually getting crushed,' said one.

Trump is said to be considering reinstating the controversial separation policy that was criticized by members of his own party and the first lady. He sees 'zero tolerance' as the one thing that worked.

A migrant caravan set out on October 13 from impoverished, violence-plagued Honduras and is headed north on the long journey through Guatemala and Mexico to the U.S.

A helicopter with the U.S. Customs and Border Protection's (CBP) Air and Marine Operations (AMO) searches in the background as a group of men from Central America are apprehended for illegally crossing into the United States from Mexico in Penitas, Texas in early October

Trump has received regular updates on the stats and has told senior policy adviser Stephen Miller, who has taken the lead on immigration issues, and Chief of Staff John Kelly that something has to change.

He tweeted about on Wednesday morning, pushing Republicans to make immigration an issue in the November election.

'Hard to believe that with thousands of people from South of the Border, walking unimpeded toward our country in the form of large Caravans, that the Democrats won't approve legislation that will allow laws for the protection of our country. Great Midterm issue for Republicans!,' he tweeted Wednesday morning.

'Republicans must make the horrendous, weak and outdated immigration laws, and the Border, a part of the Midterms!,' he added.

The president has long viewed immigration a winning issue for Republicans and partially credits his White House victory on his tough stance on the matter.

Independent political prognosticators are giving Democrats strong chances of retaking the House in November while Republicans are increasingly confident they will hold the Senate.

Immigration is an issue the president has consistently used as a hammer in his dealing with Congress and Democrats.

He has threatened to shut down the government if he doesn't getting funding to build his border wall.

Republican House Majority Leader Kevin McCarthy has prepped legislation that would fully fund the president's border wall along the U.S.-Mexico border with a $23.4 billion price tag.

But Congress is in recess until after November's election although the House could take up the matter when it returns in mid-November.

Democrats, however, oppose any legislation funding for the border wall that does not include protection for the so-called Dreamers, the children of illegal immigrants brought by their parents to the U.S. when they were young.

Trump thinks immigration can be a winning issue for Republicans

Trump sees immigration as one of issues that helped put him in the White House

Trump has threatened to cut off funding from Central American countries that don't stop their immigrants

House Democratic Leader Nancy Pelosi, who is seeking to be speaker of the House should her party retake control, said one of their first priorities would be legislation to protect Dreamers.

She also told Politico she does not see any Democrats voting to fund the wall.

'I don't see any of us voting for wall funding. … We have a responsibility to secure our borders. There are ways to do that that are consistent with civilization, humanitarianism and who we are as a nation. We have to remove all doubt about that,' she said.

And the president is gripping about a headline on an interview he gave the AP that said 'Trump tells AP he won't accept blame if GOP loses House.'

The president, when asked in the interview whether he'd 'bear some responsibility' for losses, replied, 'No, I think I'm helping people.'

'AP headline was very different from my quote and meaning in the story. They just can't help themselves. FAKE NEWS!' he tweeted without context on Wednesday.