Donald Trump cannot have obstructed justice because he is America's top law enforcement officer, his lawyers have argued according to leaked 20-page memo.

The letter sent in January from Mr Trump’s legal team to Robert Mueller, the special counsel leading the Russia investigation, was obtained by The New York Times.

It argued that Mr Trump is the country’s “chief law enforcement officer” and therefore claims of obstructing justice “would amount to him obstructing himself”.

Mr Trump’s lawyers rejected Mr Mueller’s request for an interview, saying they have already handed over documents and allowed others to talk to his team.

They also spelled out in detail why the firing of James Comey, the FBI director, and other key moments being scrutinised do not amount to obstruction of justice.

Mr Trump appeared to pre-empt publication of the revelations in a string of tweets criticising the Russia investigation on Saturday.

He said the investigation was “so bad for our country” and asked: “Is the Special Counsel/Justice Department leaking my lawyers letters to the Fake News Media?”