WASHINGTON – An aide to Vice President Mike Pence listened in on the phone call by the president that sparked an impeachment inquiry, the Washington Post reported in an article Wednesday that provides new details on Pence's involvement in the controversy.

The report said President Donald Trump used Pence in his attempt to pressure the new Ukrainian president to dig up dirt on Joe Biden, but is not conclusive on how much Pence knew about Trump's efforts.

Pence's spokeswoman, Katie Waldman, dismissed the article as an attempt to "glorify a grand conspiracy being concocted by a select number of disgruntled former employees."

Waldman said Pence's actions vindicate the administration by showing that Ukraine received military aid after Pence "directly and effectively delivered the president's anti-corruption and European burden sharing messages" to Ukrainian President Volodymyr Zelensky in a September meeting.

But the vice president's office declined to comment on whether Pence's national security adviser, retired Lt. Gen. Keith Kellogg, listened to the Zelensky call.

House Democrats on Wednesday threatened to subpoena the White House if it doesn't turn over by Friday a host of documents that include any communication Pence's office had about the July call with Zelensky.

Democrats also want information on Trump's decision not to send Pence to Zelensky's May inauguration and information on Pence's meeting with Zelensky during a trip to Poland in September.

More:Democrats threaten to subpoena White House for documents in impeachment inquiry

The document requests are part of the House's impeachment inquiry launched last week by House Speaker Nancy Pelosi, D-Calif.

The inquiry was prompted by a whistleblower complaint detailing efforts by senior White House officials to "lock down" access to records of the July call in which Trump urged his Ukrainian counterpart to investigate Biden.

At the time Trump and Zelensky spoke, the Trump administration was holding up hundreds of millions of dollars in military aid approved by Congress.

More:Poll: Only 4 in 10 Republicans think Trump mentioned Biden on Ukraine call even though he acknowledged doing so

Although Pence did not participate in the call, Kellogg was among those who monitored it, according to the Washington Post. The paper reported that Kellogg didn't hear anything he felt should be relayed to the vice president and Pence and his staff weren't aware afterward that the call had provoked alarm.

An unidentified Pence aide told the paper that his office wasn't told by the White House Counsel's Office about the whistleblower's complaint until the day before it became public.

The whistleblower's report alleged that Trump instructed Pence to cancel plans to attend Zelensky’s inauguration, a detail given in the context of Trump wanting to wait to see how the new leader “chose to act” in office.

When Pence substituted for Trump at the last minute on a trip to Poland, he had a private meeting with Zelensky. During a news conference the next day, Pence was asked whether he discussed Biden with Zelensky.

“The answer is no,” Pence said.

He gave a less direct response to the question of whether he could assure Ukraine that the hold up of military assistance was not related to efforts by Trump allies to try to investigate Biden.

Pence said Trump had asked him to talk to Zelensky “about the progress that he’s making on a broad range of areas.” That included, Pence said, steps Zelensky has taken to address public corruption and restore integrity to the public process.

The Washington Post reported that Trump sent Pence to the meeting to "take the measure" of Zelensky and let him know that military aid wouldn't be released until the administration was sure Zelensky would fight corruption. When Pence returned to Washington, he encouraged Trump to release the aid, two unidentified individuals told the Post.

The aid was released in early September.

Pence spoke by phone with Zelensky on Sept. 18, the Post reported, the same day the paper broke the news that there was a whistleblower complaint.

More:'I don't care.' Trump dismisses GOP concern over protecting whistleblower

More:As whistleblower report on Trump and Ukraine reverberates through Washington, scandal will test Pence