Vice president Mike Pence has dismissed a request by Democrats to hand over documents for the Trump impeachment probe as not being “serious”.

Democratic chairs of three committees of the House of Representatives, wrote to Mr Pence, asking him to turn over materials relating to Donald Trump’s July 25 phone conversation with Ukraine president Volodymyr Zelenskiy.

While Mr Pence did not participate on the call, and only learned about it the next day, he is said to have been briefed on the issue and was provided materials about the call.

“Recently, public reports have raised questions about any role you may have played in conveying or reinforcing the president’s stark message to the Ukrainian President,” the chairmen of the three committees wrote in a letter to Mr Pence.

“Your failure or refusal to comply with the request, including at the direction of or behest of the president or the White House, shall constitute evidence of obstruction of justice of the House’s impeachment inquiry and may be used as an adverse inference against you and the president.”

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Mr Pence has defended Mr Trump’s call. In comments earlier this week on a visit to Arizona, he said: One of the main reasons we were elected in Washington DC, was to drain the swamp.

He added: “And I think the American people have a right to know if the vice president of the United States or his family profited from his position as vice president during the last administration. That’s about looking backwards and understanding what really happened.”

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The request for Mr Pence to hand over documents, which followed subpoenas to Rudy Giuliani and Mike Pompeo, came moments before Democrats issued a subpoena to the White House. Earlier this week, they said they planned to file the subpoena if Mr Trump was not forthcoming with materials relating to the Ukraine call.

Asked on Friday whether he intended to cooperate with requests for materials, Mr Trump said: “I don’t know. That’s up to the lawyers. I know the lawyers think they’ve never seen anything so unfair. They’ve never seen anything so unjust.

“I’ve been president now for almost three years, and I’ve been going through this for almost three years. It’s almost become, like, a part of my day.”

Mr Pence’s office responded to the Democrats’ request by saying it had received the letter at the same time that it was handed to the media.