Donald Trump asked Boris Johnson for help to discredit Mueller's investigation into his alleged links to Russia.

The president asked the prime minister to help US Attorney General William Barr gather intelligence which could undermine the investigation, the Times of London reports.

The UK government denies colluding with Trump to discredit Mueller.

The president also reached out to the leaders of Ukraine, Australia, and Italy.

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Donald Trump called Prime Minister Boris Johnson earlier this year and asked him for access to British intelligence which may discredit the Mueller inquiry into the president's alleged links to Russia.

The Times of London reports that the president called Johnson on July 26 and asked him to provide the US Attorney General William Barr with evidence that may undermine the investigation.

Several days later Barr attended a meeting of the Five Eyes intelligence alliance in London where he repeated the president's suspicions about UK intelligence agencies, the paper reports.

Similar requests were also made by Trump to the leaders of Ukraine, Australia and Italy.

A spokesperson for Johnson declined on Wednesday to comment on the allegation that the president had asked the prime minister for help.

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However, asked about the allegations on Wednesday, the UK's Foreign Secretary Dominic Raab insisted that there had been no collusion between the UK and US on the issue.

"The prime minister is not going to comment on the discussions held with President Trump in private, but I can give him the assurance that of course neither the prime minister... or any member of this government would collude in the way that he described," Raab told the House of Commons.

"That is unacceptable, would never happen and did not happen."

Watch the UK Foreign Secretary deny helping discredit Mueller