U.S. President Donald Trump attends a joint press conference with visiting Finnish President Sauli Niinisto (not in the picture) at the White House in Washington D.C., the United States, on Oct. 2, 2019. (Photo by Ting Shen/Xinhua)

U.S. Ambassador to the European Union Gordon Sondland is a key witness of the controversy surrounding the July 25 phone call between President Donald Trump and Ukrainian President Volodymyr Zelensky.

WASHINGTON, Oct. 8 (Xinhua) -- Three U.S. House committees issued a joint statement Tuesday saying they will subpoena a U.S. diplomat and key witness of the Trump administration's controversial interactions with Ukraine, shortly after the Department of State blocked a congressional testimony scheduled for the same day featuring the envoy.

"We consider this interference to be obstruction of the impeachment inquiry," the chairmen of the three committees said in the statement on U.S. Ambassador to the European Union Gordon Sondland's missed testimony. "We will be issuing subpoena to Ambassador Sondland for both his testimony and documents."

The statement was issued by House Intelligence Committee Chairman Adam Schiff, Oversight and Reform Committee Chairman Elijah Cummings and Foreign Affairs Committee Chairman Eliot Engel. They have been leading an ongoing and fast-moving impeachment inquiry into President Donald Trump.

The chairmen said in the statement that they were told Tuesday morning by Scondland's personal attorneys that the State Department left a voicemail Monday night, informing the lawyers that the Trump administration would not allow the ambassador to appear at the hearing.

U.S. Secretary of State Mike Pompeo speaks during a press briefing in Washington D.C., the United States, April 22, 2019. (Xinhua/Liu Jie)

Secretary of State Mike Pompeo, in a meeting with the Estonian foreign minister Tuesday in Washington, ignored a shouted question concerning the cancellation of Sondland's testimony.

"In addition, Ambassador Sondland's attorneys have informed us that the Ambassador has recovered communications from his personal devices that the Committees requested prior to his interview today," the chairmen said in the statement. "He has turned them over to the State Department, however, and the State Department is withholding them from the Committees, in defiance of our subpoena to Secretary Pompeo."

Speaking at a press conference on Capitol Hill, Schiff called the State Department's decision to disallow Sondland to testify an "additional strong evidence of obstruction."

Schiff said that "there was no indication" that Sondland's testimony "would be a no show," and that not only the Congress, but also the American people were "being deprived of" the hearing. He added that the messages currently being withheld by the State Department "are also deeply relevant to this investigation and the impeachment inquiry."

Sondland's attorney Robert Luskin said in a letter Tuesday that his client's hearing was blocked by the State Department without an explanation.

"He is a sitting ambassador and employee of State and is required to follow their direction," Luskin said. "Ambassador Sondland is profoundly disappointed that he will not be able to testify today. Ambassador Sondland traveled to Washington from Brussels in order to prepare for his testimony and to be available to answer the Committee's questions."

Sondland is a key witness of the controversy surrounding the July 25 phone call between President Donald Trump and Ukrainian President Volodymyr Zelensky which alarmed an intelligence official, who filed a whistleblower complaint on Aug. 12 alleging Trump's misconduct on the phone.

House Speaker Nancy Pelosi announced on Sept. 24 the initiation of an impeachment inquiry into Trump. A rough transcript of the Trump-Zelensky conversation and a redacted version of the whistleblower complaint were released in the following two days.

House Democrats probing the matter believed Trump pressured Zelensky to investigate, among others, Joe Biden, a Democratic presidential candidate for the 2020 U.S. election. Trump has said that no pressure was put on his Ukrainian counterpart, and that his call for the investigation has nothing to do with Biden's campaign.

Documents containing text messages between U.S. and Ukrainian officials submitted to Congress Thursday by former U.S. special envoy to Ukraine, Kurt Volker, showed that Sondland was involved in coordinating Washington's engagement with Zelensky's government before and after the presidential phone call. Zelensky, a former comedian, assumed office on May 20.

"Ambassador Sondland believes strongly that he acted at all times in the best interests of the United States, and he stands ready to answer the Committee's questions fully and truthfully," Luskin said in the letter.

Trump in a tweet Tuesday said he "would love to send" Sondland to testify, "but unfortunately he would be testifying before a totally compromised kangaroo court, where Republican's rights have been taken away, and true facts are not allowed out for the public to see."

In a subsequent tweet, Trump cited a tweet by Sondland as saying the president's intentions in his call with Zelensky were "incorrectly" perceived. "The President has been crystal clear: no quid pro quo's of any kind," Trump quoted his EU envoy's assertions, adding "That says it all!"

Sondland's testimony is "based on the unfair and partisan process that Mr. Schiff has been running," Jim Jordan, Republican Ranking Member of the Oversight and Reform Committee, said Tuesday on Capitol Hill.

As part of the impeachment inquiry, Sondland and Volker, along with three other State Department officials, were asked for depositions by a congressional subpoena issued Sept. 27 to Pompeo. Sondland's deposition was set for Thursday while Volker resigned before the Oct. 3 deadline imposed on him. ■