Trump's border wall tumbles under Biden

Former US president Donald Trump's signature border wall would lose much of its funding, as well as the fast-track status that enabled it to bypass environmental regulations, under a new plan announced by the Biden administration.

President Joe Biden suspended construction of the wall upon taking office while his administration reviewed the project, angering Republicans in Congress eager to see it go forward amid growing apprehension of migrants along the southwest border.

The plan announced on Friday does not cancel the wall project outright, but is still likely to face opposition in Congress, where many Republicans are eager to promote a project closely associated with the former president.

Biden plans to return more than $US2 billion ($A2.6 billion) that the Trump administration diverted from the Pentagon to help pay for the wall, and use other money appropriated by Congress to address "urgent life, safety, and environmental issues" created by the construction.

It also asks lawmakers not to provide any additional funding for what the Biden team believes is an unnecessary effort.

"Building a massive wall that spans the entire southern border and costs American taxpayers billions of dollars is not a serious policy solution or responsible use of federal funds," the Office of Management and Budget said in a statement outlining the plan.

The government has built walls and other barriers along the 3200km US-Mexico border for decades to eliminate some of the easier routes of avoiding checkpoints.

Trump turned the issue into a centerpiece of his political identity.

The former president vowed to build a "virtually impenetrable" wall, insisting it would be paid for by Mexico, which never happened.

Instead, his administration set aside about $US15 billion ($A19 billion) through a combination of congressional appropriations and taking the money from the Pentagon and other parts of the government.

The Trump administration built about 725km of wall, waiving requirements for environmental reviews and mediation, though only about 84km were in areas where no barrier previously existed.