WASHINGTON – House Democrats threatened to subpoena the White House in an escalating battle over documents and witness testimony in the impeachment inquiry into President Donald Trump's dealings with Ukraine.

The chairmen of three committees said in a joint statement Wednesday that the administration must release documents by Friday.

Rep. Elijah Cummings, D-Md., chairman of the House Committee on Oversight and Reform, said the White House has “refused to engage with – or even respond to” the committees’ requests.

“The White House’s flagrant disregard of multiple voluntary requests for documents – combined with stark and urgent warnings from the Inspector General (of the intelligence community) about the gravity of these allegations – have left us with no choice but to issue this subpoena,” Cummings wrote in a memo to committee members that was released along with a draft subpoena.

Trump attacked House Intelligence Committee Chair Adam Schiff and House Speaker Nancy Pelosi when asked Wednesday whether he'd comply.

"I always cooperate. This is a hoax," Trump said during an afternoon news conference with Finland's president. “But we’ll work together with Shifty Schiff and Pelosi and all of them, and we'll see what happens.”

Earlier, Trump live-tweeted a news conference held by Pelosi and Schiff soon after the draft subpoena was released.

Trump challenged Pelosi's stated desire to work on issues such as trade and drug prices, saying Democrats are too obsessed with impeachment.

Pelosi is "incapable" of working on other issues, Trump tweeted. "It is just camouflage for trying to win an election through impeachment. The Do Nothing Democrats are stuck in mud!"

Pelosi said Democrats can work with the administration on infrastructure, drug costs and other issues.

“Clean government?” she added. “That’s more of a challenge.”

Tuesday, Secretary of State Mike Pompeo pushed to delay testimony by five State Department officials whom House Democrats asked to depose. He accused Democrats of trying to "intimidate" and "bully" career professionals in their quest to impeach Trump.

Wednesday, Pompeo acknowledged he listened in on the controversial phone call between Trump and Ukraine's leader, Volodymyr Zelensky – a conversation that sparked the House Democrats' impeachment inquiry.

That call prompted a whistleblower to file an anonymous complaint alleging that Trump was "using the power of his office to solicit interference from a foreign country in the 2020 U.S. election."

Rudy Giuliani, Trump's personal attorney, publicly acknowledged that he pressed Ukrainian government officials to open an investigation into former Vice President Joe Biden, a leading candidate for the 2020 Democratic presidential nomination. He said he contacted Ukrainian officials at the direction of the State Department and he briefed U.S. diplomats on his conversations.

House Democrats opened the impeachment inquiry last week, focused on probing the "extent to which President Trump may have jeopardized national security" by pressing Ukraine to investigate Biden and by withholding military assistance to help Ukraine counter Russian aggression.

“We’re not fooling around here,” Schiff said Wednesday. “It’s hard to imagine a more corrupt course of conduct.”

Schiff repeated a warning Democrats have made that attempts by the White House to block the investigation will be considered evidence of obstruction and will imply that the allegations being investigated "are, in fact, correct."

If the White House isn't forthcoming, Schiff said, Democrats "will have to decide whether to litigate or how to litigate."

"We don't want this to drag on months and months and months, which appears to be the administration's strategy," he said.

Democrats subpoenaed Pompeo for documents last week and issued a subpoena to Giuliani on Monday.

“She hands out subpoenas like they're cookies,” Trump said of Pelosi. " 'You want a subpoena? Here you go. Take them.' Like they're cookies."

Cummings' memo to other members of the committee said there's no time for the panel to vote on the subpoena "without causing undue delay to the investigation" since lawmakers are in a two-week recess. Instead, Cummings said, the subpoena will be issued under the rules of the House in consultation with the leaders of the House foreign affairs and intelligence committees, which are also investigating Trump.

Cummings said he is "seeking feedback" from lawmakers who are requested "to provide any information they would like to be considered on their positions with respect to this subpoena."

Contributing: Deirdre Shesgreen