House committees conducting an impeachment inquiry into President Donald Trump want Vice President Mike Pence to turn over any documents he might have about the president's attempts to get Ukraine to investigate former Vice President Joe Biden and the 2016 U.S. election.

"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 heads of the House Intelligence, Oversight and Foreign Affairs committees wrote in a letter Friday.

The letter notes references in those reports to a member of Pence's staff who may have participated directly in the July call at the heart of the controversy; documents Pence may have seen, including a record of the call; and Pence's own September meeting with the Ukrainian president in Warsaw, "during which you reportedly discussed the Administration’s hold on U.S. security assistance to Ukraine.”

It asks that he turn over the documents by Oct. 15.

Failure to do so "shall constitute evidence of obstruction of the House's impeachment inquiry and may by used as an adverse inference against you and the president," the letter signed by Democratic Reps. Adam Schiff, Eliot Engel and Elijah Cummings says.

Pence's office derided the request as a public relations ploy. “The Office of the Vice President received the letter after it was released to the media and it has been forwarded to Counsel’s Office for a response," Katie Waldman, the vice president's press secretary, said in a statement. "Given the scope, it does not appear to be a serious request but just another attempt by the Do Nothing Democrats to call attention to their partisan impeachment."

The impeachment inquiry is centered on the July phone call Trump had with Volodymyr Zelenskiy in which he asked the Ukrainian president to investigate Democrat Joe Biden and his son.

Trump offered up Pence as a possible witness while talking to reporters last week, noting that the VP had also spoken to Zelenskiy and that reporters should look at a transcript of their talks.

“I think you should ask for Vice President Pence’s conversation, because he had a couple of conversations also,” Trump said. He said Pence's conversations, like his, were "perfect."

Democrats maintain Trump's call was illegal because he was inviting a foreign leader to take action against a political rival.

Pence told reporters Thursday he never discussed the Bidens with Zelenskiy, but they had spoken about "corruption" in the country in general.

"Well, as I said the day after that meeting, we focused entirely, in my meeting with President Zelenskiy of Ukraine, on the issues that President Trump has raised as a concern, namely the lack of support from European partners for Ukraine and real issues of corruption in Ukraine," Pence said.

The letter marked the latest request from these three committees as part of the impeachment inquiry, which has issued a host of document and testimony requests and subpoena threats over the past week to a string of departments, officials and individuals including Secretary of State Mike Pompeo and the president's lawyer, Rudy Giuliani.