Donald Trump's personal attorney Rudy Giuliani has been subpoenaed for documents related to his work in Ukraine on behalf of the president, marking the latest escalation of the impeachment inquiry launched by House Democrats just last week.

The subpoena follows after the release of a bombshell whistleblower complaint, which claims Mr Trump urged the leader of Ukraine to open an investigation into former vice president Joe Biden, a potential 2020 political rival.

During the 25 July phone call between Mr Trump and Ukraine's Volodymyr Zelensky, according to that complaint and a transcript released by the White House, the president urged his Ukrainian counterpart to consult with Mr Giuliani in that investigation.

"Our inquiry includes an investigation of credible allegations that you acted as an agent of the President in a scheme to advance his personal political interests by abusing the power of the Office of the President," the letter to Mr Giuliani from the chairmen of three House committees — the Intelligence, Foreign Affairs, and Oversight and Reform Committees — reads.

Those chairmen named on the letter are representatives Adam Schiff, Eliot Engel, and Elijah Cummings, respectively. Mr Giulani now has until 15 October to comply with the subpoena.

"Your failure or refusal to comply with the subpoena, including at the direction or behest of the President or the White House, shall constitute evidence of obstruction of the House's impeachment inquiry and may be used as an adverse inference against you and the President," the letter, which references numerous instances in which Mr Giuliani has openly discussed efforts to compel Ukraine to launch "politically-motivated" investigations, says.

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The subpoena comes after a weekend packed with political posturing on both sides of the impeachment divide, including frequent appearances by Mr Giuliani himself on cable news to make the case for his client. Mr Giuliani, who has shown himself to be a scrappy defender of the president, even went as far on Sunday as to say he would not cooperate with any investigation by Mr Schiff — only to contradict himself moments later and during the same interview.

“I wouldn’t cooperate with Adam Schiff,” he said Sunday during an interview with ABC News's George Stephanopoulos. “I think he should be removed. If they remove Adam Schiff and put a neutral person in, a Democrat who hasn’t expressed an opinion — if I had a judge in the case and announced he was going to impeach, wouldn’t I move to recuse that judge.”

When the host pressed him — "you're not going to cooperate?" — Mr Giuliani shot back, indicating he will comply with whatever Mr Trump wants: "I didn't say that. I said I would consider it."

The subpeona released Monday cites a separate interview of Mr Giuliani's as an example, as well. That interview, from 19 September, occurred on CNN.

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"So, you did ask Ukraine to look into Joe Biden," CNN's Chris Cuomo asked him then.

Mr GIuliani responded: "Of course I did."