Donald Trump is expected to divert billions of dollars more to building the border wall that he repeatedly claimed would be paid for by Mexico.

While his 2021 budget proposals, to be unveiled this week, will request $2 billion for the anti-immigration barrier, less than in previous years, the homeland security department could take billions more from the Pentagon, according to reports.

CNN also reported a senior defence official saying a major announcement on the wall would be made this week.

A "big, beautiful" wall was one of the centerpieces of Mr Trump's 2016 campaign, one which he repeatedly promised would be paid for by Mexico – which has flatly refused to do so.

Congress is responsbile for government spending but the president's priorities will be seen as politically significant ahead of his reelection bid in November.

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As well as money for the border wall, he is expected to propose up to $4.6 billion in spending cuts over the next 10 years, much of it from programmes like Medicaid, disability insurance and food stamps.

Government data seen by the Washington Post suggested the Trump administration was a long way from completing the 500 miles of new barriers the president had promised would be in place by 2021.

Most of what has been built is considered to be replacement fencing because building new sections of wall often requires the acquisition of private land.

Homeland security officials have said they will have 450 miles either finished or under construction by the end of 2020.

Last year the president took $2.5 billion from the military budget's anti-drug programme for the wall.

This year that figure could be much higher, with the Washington Post claiming as much as $7.2 billion could be diverted from the Pentagon help build the wall.