Mueller threatened to subpoena Donald Trump over Russia probe

Special Counsel Robert Mueller has warned he could issue a subpoena for Donald Trump to appear before a grand jury as part of a probe into alleged Russian meddling in the 2016 election, US media report.

Mueller suggested the move during talks with Trump's lawyers in March.

He said the subpoena would compel the president to face investigators, the Washington Post reports.

Mueller discussed a subpoena in a meeting in early Marchbefore John Dowd, the lead outside attorney advising Trump on the Russia investigation, stepped down.

It is believed to be the first time the special counsel raised the possibility of forcing Trump to testify.

During the meeting in March, Trump's lawyers insisted that the president was under no obligation to face questions by federal investigators in relation to the Russia inquiry, according to the Washington Post, which cited four people familiar with the encounter.

However Mueller's team reportedly responded by suggesting they would issue a subpoena if Trump declined. They agreed to provide the president's lawyers with more specific information about the questions they wished to ask Trump.

On Monday, the president criticised the New York Times for publishing more than 40 questions that Mueller wanted to ask him as part of the Russia investigation.

Mueller also plans to ask Trump about his election campaign's possible co-ordination with Russia, according to the New York Times, which said it obtained the list from someone other than the president's lawyers.

He tweeted on Tuesday that the leaking of the inquiry questions to the media was "disgraceful", adding: "It would seem very hard to obstruct justice for a crime that never happened."

Trump's personal attorney, Jay Sekulow, said Tuesday night: "We do not discuss conversations we have or have not had with the Office of Special Counsel." Ty Cobb, a member of Trump's White House legal team, had no comment. The Post reported that a spokesman for Mueller declined to comment.

White House spokesman Raj Shah said the Times report was "troubling".

"The entire premise of this investigation was on this topic of collusion and the overwhelming focus of the questions is not on that topic," he said.

The special counsel is looking into Russia's efforts to interfere in the 2016 US election, whether there was any collusion between the Kremlin and Trump's election campaign and whether the president unlawfully tried to obstruct the inquiry.