A top US diplomat reportedly told Donald Trump’s personal lawyer that claims about Joe Biden having acted corruptly in Ukraine “were not credible”.

Kurt Volker, the former special envoy to Ukraine who is named in the whistleblower complaint as having been told to “contain the damage” caused by Rudy Giuliani’s outreach to Ukraine’s president, told members of Congress he had warned the one-time New York mayor he was receiving incorrect information about Mr Biden.

The Washington Post reported that Mr Volker, who last month quit his post as special envoy after being named in the compliant that accused Mr Trump of seeking Ukraine’s help in the 2020 election, told a closed door hearing on Capitol Hill that Mr Giuliani should not trust stories told to him by that country’s former top prosecutor.

Mr Giuliani, who on Monday was issued a subpoena by Democrats seeking information about his outreach to Ukraine president Volodymyr Zelensky, and other officials from the country, has admitted acting on behalf of the president in pushing for a probe into the force vice president and his son, Hunter.

The Post said that at the heart of the issue has been Mr Giuliani’s claim that while he was vice president, Mr Biden pushed for the firing of Ukraine’s former prosector general, Viktor Shokin, as part of a corrupt plot to halt investigations into a Ukrainian natural gas company that employed Hunter Biden.

Ukraine Elections 2019 in pictures Show all 26 1 /26 Ukraine Elections 2019 in pictures Ukraine Elections 2019 in pictures Volodymyr Zelenskiy, centre right, and his wife Olena Zelenska, greet supporters after exit polling gave the comedian a commanding lead AP Ukraine Elections 2019 in pictures Outgoing Ukrainian President Petro Poroshenko raises his hand with his wife Maryna at his party headquarters in Kiev AFP/Getty Images Ukraine Elections 2019 in pictures Ukrainian presidential candidate Volodymyr Zelenskiy reacts following the announcement of the first exit poll REUTERS Ukraine Elections 2019 in pictures Comedian and leading Ukrainian presidential candidate Volodymyr Zelenskiy plays ping pong with a journalist at his election night gathering in Kiev, Ukraine. If no candidate receives more than 50% of the vote, the top two vote-getters will face off in a second-round election on April 21 Getty Ukraine Elections 2019 in pictures Election officials count ballots at a polling station in Kiev during the first round of Ukraine's presidential election, AFP/Getty Ukraine Elections 2019 in pictures People walk in front of St. Sophia Cathedral in Kiev during Ukraine's presidential election AFP/Getty Ukraine Elections 2019 in pictures Ukrainian servicemen sit in a truck to head to a polling station, near the front line with pro-Russian separatists, near Butivka, Donetsk region AFP/Getty Ukraine Elections 2019 in pictures Ukrainian citizens living in Kyrgyzstan vote in Ukraine's presidential election at a polling station in the Ukrainian embassy in Bishke AFP/Getty Ukraine Elections 2019 in pictures Ukrainian citizens living in Kyrgyzstan vote in Ukraine's presidential election at a polling station in the Ukrainian embassy in Bishkek AFP/Getty Ukraine Elections 2019 in pictures Ukrainian citizens living in Kyrgyzstan vote in Ukraine's presidential election at a polling station in the Ukrainian embassy in Bishkek AFP/Getty Ukraine Elections 2019 in pictures Ukrainian citizens living in Kyrgyzstan vote in Ukraine's presidential election at a polling station in the Ukrainian embassy in Bishkek AFP/Getty Ukraine Elections 2019 in pictures A young girl casts the ballot of a man at a polling station in Kiev on the first round of Ukraine's presidential election, on. Exit polls are expected when voting stations close at 8 pm local time (1700 GMT). First preliminary results are expected several hours after. Barring a shock result in which one candidate crosses the 50 percent threshold in the first round, a run-off will be held on April 2 AFP/Getty Ukraine Elections 2019 in pictures Ukrainian comic actor, showman and presidential candidate Volodymyr Zelensky waves in front of voting booths at a polling station during Ukraine's presidential election in Kiev AFP/Getty Ukraine Elections 2019 in pictures Former Ukrainian Prime Minister and presidential candidate Yulia Tymoshenko speaks with the media after casting her ballot at a polling station during Ukraine's presidential election in Kiev AFP/Getty Ukraine Elections 2019 in pictures Former Ukrainian Prime Minister and presidential candidate Yulia Tymoshenko speaks with the media after casting her ballot at a polling station during Ukraine's presidential election in Kiev AFP/Getty Ukraine Elections 2019 in pictures Former Ukrainian Prime Minister and presidential candidate Yulia Tymoshenko speaks with the media after casting her ballot at a polling station during Ukraine's presidential election in Kiev AFP/Getty Ukraine Elections 2019 in pictures Ukrainian comic actor, showman and presidential candidate Volodymyr Zelensky casts his ballot at a polling station during Ukraine's presidential election in Kiev AFP/Getty Ukraine Elections 2019 in pictures Ukrainian comic actor, showman and presidential candidate Volodymyr Zelensky gestures in front of voting booths at a polling station during Ukraine's presidential election in Kiev AFP/Getty Images Ukraine Elections 2019 in pictures Ukrainian comic actor, showman and presidential candidate Volodymyr Zelensky walks with his ballot at a polling station during Ukraine's presidential election in Kiev AFP/Getty Images Ukraine Elections 2019 in pictures A view of the building of the Ukrainian Central Election Commission in Kiev during Ukraine's presidential election. AFP/Getty Ukraine Elections 2019 in pictures Ukrainian President Petro Poroshenko (L) casts his ballot at a polling station in Kiev on the first round of Ukraine's presidential election, The 53-year-old president has positioned himself during the political campaign as the only person able to stand up to the Kremlin and has promised to return Crimea to Ukraine if he is re-elected. AFP/Getty Ukraine Elections 2019 in pictures A voter emerges from the voting booth after filling out her ballot for Ukraine's presidential election in Kiev, Ukraine. If no candidate receives more than 50% of the vote, the top two vote-getters will face off in a second-round election on April 21. Getty Ukraine Elections 2019 in pictures Ukrainian president Petro O. Poroshenko (C), running for re-election, receives his ballot in Ukraine's presidential election on in Kiev, Ukraine. If no candidate receives more than 50% of the vote, the top two vote-getters will face off in a second-round election on April 21 Getty Ukraine Elections 2019 in pictures A woman holds her ballot as she leaves a voting booth at a polling station in Kiev on the first round of Ukraine's presidential election. - Exit polls are expected when voting stations close at 8 pm local time (1700 GMT). First preliminary results are expected several hours after. Barring a shock result in which one candidate crosses the 50 percent threshold in the first round, a run-off will be held on April 21 AFP/Getty Ukraine Elections 2019 in pictures A young girl casts the ballot of a man at a polling station in Kiev on the first round of Ukraine's presidential election. Exit polls are expected when voting stations close at 8 pm local time (1700 GMT). First preliminary results are expected several hours after. Barring a shock result in which one candidate crosses the 50 percent threshold in the first round, a run-off will be held on April 21 AFP/Getty Ukraine Elections 2019 in pictures Ukrainian servicemen queue to cast their ballots at a polling station near the front line line with pro-Russian separatists near Avdiivka, Donetsk region, during the first round of Ukraine's presidential election AFP/Getty

Mr Biden has repeatedly denied any wrongdoing, and independent experts have pointed out the vice president’s efforts were part of a broader international effort that included the European Union and the International Monetary Fund. A number of senior officials there had little time for Mr Shokin.

Mr’s Volker’s comments appear to be at odds with comments made earlier in the day by Republican members of the House who attended Thursday’s closed-door session.

Congressman Jim Jordan of Ohio, told CNN “not one thing” the ex-diplomat said “aligns with the “Democratic impeachment narrative”.

Rudy Giuliani contradicts himself after claiming he would not cooperate with impeachment investigation

Mr Volker spent the morning testifying behind closed-doors before members from multiple House committees. Mr Jordan said House intelligence chairman Adam Schiff limited members from asking questions.

“We have never seen a chairman suggest that members aren’t allowed to ask questions. So, if this is how Mr Schiff is going to conduct these kinds of interviews.....that’s a concern as well,” he said.

Mr Jordan said Mr Volker had been “very impressive”, but would not elaborate on the specifics.

On Twitter, Mr Giuliani launched another attack on Democrats.

“Democrats now own Biden corruption,” he said