Secretary of State Mike Pompeo on Tuesday pushed back against a request by a key House committee to interview five current or former State Department officials as part of an impeachment inquiry centering on the Ukraine scandal, accusing House Democrats of attempting to “intimidate" and "bully" them.

“I am concerned with aspects of your request … that can be understood only as an attempt to intimidate, bully, and treat improperly the distinguished professionals of the Department of State, including several career Foreign Service Officers, whom the committee is now targeting,” Pompeo wrote in a letter to House Foreign Affairs Chairman Eliot Engel, D-N.Y.

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“Let me be clear: I will not tolerate such tactics, and I will use all means at my disposal to prevent and expose any attempts to intimidate the dedicated professionals whom I am proud to lead and serve alongside at the Department of State,” Pompeo wrote.

Pompeo’s letter was in response to a request by Engel and other key chairmen to depose the current or ex-State Department officials about the Ukraine scandal engulfing the Trump administration. House Democrats have seized upon the scandal to launch the formal impeachment inquiry into President Donald Trump.

The secretary of state appeared to dare Engel to issue subpoenas for the appearance of the five officials, writing that “the committee has not issued any subpoenas for depositions and we are not aware of any other authority by which the committee could compel appearance at a deposition.”

He also took issue with the “woefully inadequate opportunity"that Engel and committee members had given "the Department and the requested witnesses" to prepare for an interview.

Pompeo claimed the officials would need more time to retain and consult with private counsel and said the State Department "must consult" with them and their lawyers "regarding the Department’s legitimate interests in safeguarding potentially privileged and classified information."

House Democrats had scheduled the five depositions over this week and next. The witnesses they're seeking to interview include the former U.S. ambassador to Ukraine, Marie Yovanovitch, who was abruptly ousted from her post in May, and the former U.S. special envoy to Ukraine, Kurt Volker, who resigned last week.

In his response, Pompeo wrote, "Given the serious substantive and procedural deficiencies in the Committee’s requests … the Committee’s assertion lacks any recognized legal basis."

Citing the Democrats' warning in the letter that said the failure of the officials to appear for depositions would "constitute evidence of obstruction," Pompeo disputed any legal backing for the threat and added, "I urge you to exercise restraint in making such unfounded statements in the future."

"The Committee’s requested dates for depositions are not feasible," he wrote. "The Department will be in further contact with the Committee in the near future as we obtain further clarity on these matters."

Yovanovitch, who was previously scheduled for a joint deposition before the House Intelligence, Foreign Affairs and Oversight committees on Wednesday, will now appear Oct. 11 with the agreement of both the committees and counsel, two committee aides told NBC News.

The former Ukrainian ambassador is fulfilling an assignment at Georgetown University but remains in the foreign service, putting her in "an impossible situation," a Democratic aide whose boss sits on one of the investigating committees acknowledged.

Volker will appear Thursday for a joint deposition before the three committees, two committee aides told NBC News Tuesday.

Pompeo, meanwhile, faces a Friday deadline to turn over documents related to Trump's July 25 call with Ukrainian President Volodymyr Zelenskiy that were subpoenaed by Engel and two other top House Democratic chairmen.

NBC News confirmed Monday that Pompeo was on that phone call.

In his letter Tuesday, Pompeo acknowledged "receipt of the subpoena" and said the State Department "intends to respond to that subpoena by the noticed return date of October 4, 2019.”

The State Department’s Office of Inspector General is planning to brief staff from a number of House and Senate committees about documents related to the State Department and Ukraine, multiple Congressional sources told NBC News.

Last Friday, Engel, as well as House Intelligence Chairman Adam Schiff, D-Calif, and House Oversight Chairman Elijah Cummings, D-Md., wrote a letter demanding that Pompeo turn over documents related to the July 25 call.

The subpoena, which was issued by the Foreign Affairs Committee in consultation with the other two panels, is the first since House Speaker Nancy Pelosi launched the formal impeachment inquiry last week.

In a joint statement later Tuesday, the three chairmen accused the secretary of state of himself "intimidating Department witnesses in order to protect himself and the President."

“Secretary Pompeo was reportedly on the call when the President pressed Ukraine to smear his political opponent," they said. "If true, Secretary Pompeo is now a fact witness in the House impeachment inquiry. He should immediately cease intimidating Department witnesses in order to protect himself and the President."

“Any effort to intimidate witnesses or prevent them from talking with Congress — including State Department employees — is illegal and will constitute evidence of obstruction of the impeachment inquiry," they added.