US President Joe Biden visited the US-Mexico border in February
US President Joe Biden visited the US-Mexico border in February AFP

US President Joe Biden is expected to announce steps Tuesday to close the Mexican border to asylum seekers when numbers surge, in a bid to tackle a key weak spot in his election battle with Donald Trump.

Biden, 81, is set to sign a long-awaited executive order that would allow officials at certain times to deport migrants who cross the border illegally without processing their asylum claims first, US media reported.

The move would be one of the toughest ever by a Democratic president, and see him moving further towards Republican Trump's own signature border policies, amid polls showing the issue drags on Biden's reelection chances in November.

An announcement is expected on Tuesday, sources close to the matter said, although the White House would not confirm reports that Biden will sign the executive order alongside mayors from border towns.

"What I can say is we are constantly and continuously looking at all options to try and really deal with the immigration system, a system that's been broken for decades," Press Secretary Karine Jean-Pierre said on Monday.

Jean-Pierre blamed Republicans in Congress for failing to cooperate with Biden, and for blocking billions of dollars in funding for the border which the president tried to push through along with money for Ukraine and Israel.

"They decided to pick partisan politics," she said.

Biden's curbs on asylum requests would kick in when illegal crossings hit 2,500 a day, and would not lift until numbers drop back to 1,500, several US media outlets reported.

But he faces opposition on several fronts.

The plans could anger some Democrats as they are the toughest by his party for years, and would rely on the use of the same law that Trump's administration used to ban immigration from some Muslim countries.

They would also almost certainly be challenged in court.

Republicans have sought to make the border a key issue ahead of the November 5 vote, portraying Biden as soft on stopping what Trump calls an "invasion" of migration.

More than 2.4 million migrants crossed the southern US border in 2023 alone, largely from Central America and Venezuela as they flee poverty, violence and disasters exacerbated by climate change.

The figure rose to a record high of 10,000 a day in December and, while it has fallen dramatically in recent months, polls show the issue is one of Biden's biggest liabilities in the election.

Trump spent his time in office trying to build a wall on the Mexican border and has drastically ramped up his anti-immigration rhetoric as he seeks a White House comeback.

He has repeatedly spoken of migrants "poisoning the blood" of the United States and raised the possibility of mass repatriations by the US military and detention camps.

Trump and his allies have also accused Biden of operating an open border policy to boost Democratic voter numbers -- an allegation that Democrats decry as a racist conspiracy theory.

Biden's administration has tried to curb crossings by working with Mexico and other countries to reduce migrant flows through enforcement and economic policies, but many voters appear to think he took his eye off the ball.

The US president's announcement is due just a day after he spoke with Claudia Sheinbaum, who was elected Mexico's first woman president, to offer his congratulations and pledge a "strong and collaborative partnership".