WASHINGTON, Oct. 8 (Xinhua) -- A U.S. House committee on Tuesday subpoenaed Gordon Sondland, U.S. ambassador to the European Union, after the State Department blocked the diplomat's congressional testimony scheduled for the same day.

Sondland should have explained his knowledge about the Trump administration's controversial interactions with Ukraine at the hearing arranged by House Intelligence, Oversight and Reform and Foreign Affairs committees. The committees have been leading -- and are speeding up -- an impeachment inquiry into U.S. President Donald Trump.

The subpoena, issued by the Intelligence panel in consultation with the other two committees, requested that Sondland produce documents by Oct. 14.

It also urged him to appear at a deposition on Oct. 16, after he failed to show up Tuesday. A request for Sondland's removal was sent accompanying a Sept. 27 subpoena to Secretary of State Mike Pompeo by the committees.

"In light of Secretary Pompeo's direct intervention to block your appearance before our committees, we are left with no choice but to compel your appearance at a deposition pursuant to the enclosed subpoena," Intelligence Committee Adam Schiff, Foreign Affairs Committee Chairman Eliot Engel and Oversight Chairman Elijah Cummings wrote in a letter to Sondland.

Sondland's attorney Robert Luskin said in a letter earlier Tuesday that the State Department prohibited his client from attending the hearing without an explanation, and that Sondland "is profoundly disappointed that he will not be able to testify today."

Shortly after being informed of the State Department's decision, the three chairmen issued a joint statement saying they will subpoena Sondland.

They said they were told by Sondland's attorneys that the ambassador "has recovered communications" related to the Ukraine controversy "from his personal devices that the Committees requested."

Sondland, the chairmen added, turned the materials over to the State Department, which, however, "is withholding them from the Committees, in defiance of our subpoena to Secretary Pompeo."

Sondland is a key witness of the controversy surrounding a phone call on July 25 between 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 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.