Robert Mueller is seeking documents on Trump's most controversial decisions as President

Special counsel Robert Mueller is said to have asked the White House for documents regarding some of Donald Trump’s most controversial actions since becoming president, including his firing of ex-FBI Director James Comey.

Mr Mueller’s probe into potential ties between Russia and the Trump campaign appears to have heated up in recent weeks, with the special investigator also reportedly asking the White House if he can interview staffers as well as current and former top aides to the President.

Mr Mueller’s latest request for documents, as reported by the New York Times, indicates that several aspects of Mr Mueller’s investigation focus on Mr Trump’s conduct in the White House.

According to the Times, Mr Mueller is also interested in scrutinising Mr Trump’s meeting with Russian officials in which the President reportedly said the dismissal of Mr Comey had relieved “great pressure” on him.

Mr Mueller has also requested documents about the circumstances of the firing of former National Security Adviser Michael Flynn, the Times said.

In January, White House counsel Don McGahn was briefed by then-Deputy Attorney General Sally Yates that Mr Flynn could be susceptible to blackmail by the Russian government. Mr Flynn wasn't forced out of the White House until about three weeks later, after it was revealed that he had misled Vice President Mike Pence about his communications with a Russian official, Ambassador Sergey Kislyak.

Mr Mueller is trying to determine if Mr Trump's campaign advisers colluded with the Russian government to influence the 2016 presidential election. That investigation also reportedly involves a probe into whether the President obstructed justice when he allegedly asked Mr Comey to drop an inquiry into Mr Flynn's possible ties to Russia.

According to the Times, Mr Mueller has also asked for information regarding how the White House responded to questions from the newspaper about a meeting Mr Trump’s eldest son, Donald Trump Jr, had with a Kremlin-connected attorney last year.

One of Mr Trump’s lawyers, Ty Cobb, told the Times: “We can’t comment on any specific requests being made or our conversations with the special counsel.’’