Donald Trump said he prevented the US ambassador to the European Union, Gordon Sondland, from testifying to congressional impeachment hearings, calling them a “kangaroo court”.

Democrats leading the impeachment investigation said Sondland’s lawyers were called by a state department official after midnight, leaving a voicemail message ordering him not to attend Tuesday’s hearings.

The late night call came after Sondland handed over WhatsApp messages and other communications from his personal devices to the state department, which was refusing to provide them to the House committees holding the impeachment hearings.

“Ambassador Sondland’s testimony and documents are vital, and that is precisely why the administration is now blocking his testimony and withholding his documents,” the chairs of the House intelligence, oversight and foreign affairs committees said in a written statement

“We consider this interference to be obstruction of the impeachment inquiry,” the statement said, adding that the committees would be issuing subpoenas to Sondland for his testimony and documents.

Sondland had been due to testify voluntarily on his communications with Ukrainian officials, US diplomats, the president and the president’s lawyer, about the time of Trump’s 25 July phone call with the Ukrainian president, Volodymyr Zelinskiy. At issue is the question of whether Trump abused his office by using its power to his own political advantage, by pushing a Ukrainian investigation of Joe Biden, a likely opponent in the 2020 election.

Sondland’s attorney, Robert Luskin, said his client had been eager to answer questions from the House committees, but had been instructed by the state department early on Tuesday not to attend.

Later in the morning, Trump went on Twitter to say he ordered Sondland to be blocked.

“I would love to send Ambassador Sondland, a really good man and great American, to testify, but unfortunately he would be testifying before a totally compromised kangaroo court, where Republicans’ rights have been taken away, and true facts are not allowed out for the public to see,” the president tweeted.

Republicans are pushing for equal rights as the minority party to issue subpoenas, and the White House has said it will not respond to subpoenas until such rights are granted.

“Ambassador Sondland is profoundly disappointed that he will not be able to testify today,” Luskin’s statement read, adding that he had travelled to Washington from Brussels to prepare for his testimony.

Adam Schiff, the Democratic chair of the House intelligence committee, said Sondland was “an important witness”, adding: “We will consider this act today … as well as withholding information … to be further acts of obstruction.”

“The American people have the right to know if the president is acting in their interests, in the nation’s interest, and not in his narrow personal, political interests,” Schiff told reporters after the presidential tweets. “Indeed, the American people have a need to know.”

Luskin, Sondland’s lawyer, said the ambassador “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.

He added: “Ambassador Sondland hopes that the issues raised by the state department that preclude his testimony will be resolved promptly. He stands ready to testify on short notice, whenever he is permitted to appear.”

In his morning tweets, Trump pointed to a text message Sondland had sent to the acting US ambassador in Ukraine (which Trump misidentified as a tweet), in which Sondland said: “I believe you are incorrect about President Trump’s intentions. The president has been crystal clear: no quid pro quo’s of any kind.”

However, Sondland’s previous text exchanges with US officials, released by the House committees, made clear that Zelenskiy would not get a coveted White House visit unless he launched the investigations Trump was demanding.

Ukraine is not in the European Union, but Sondland was dispatched to work alongside the Ukraine special envoy Kurt Volker, apparently in the capacity as a direct emissary of the president, to persuade Ukraine to co-operate.

The two men also consulted Rudy Giuliani, Trump’s personal attorney, who was working on the Ukraine matter.

Volker resigned his post before testifying to the House committees last week.

The White House appears to have calculated that Sondland’s testimony might be more damaging than facing the wrath of the House over his absence. Sondland, a wealthy Oregon hotelier, was named ambassador to the EU last year after donating $1m to Trump’s inauguration fund.

Congress is on recess but committees investigating the president continue to work.

A new Washington Post/Schar School poll released on Tuesday showed 58% support for the impeachment inquiry and 49% support for moving to impeach the president and attempting to remove him from office.