A close associate of Donald Trump’s personal lawyer has claimed the US president “knew exactly what was going on” regarding the situation in Ukraine.

Lev Parnas alleged that he delivered an ultimatum in May to the incoming president of Ukraine that no senior US officials would attend his inauguration and all American aid to the country would be withheld if an investigation into Joe Biden was not announced.

Mr Parnas, an associate of Rudy Giuliani, made several potentially explosive claims in a television interview.

The day after Mr Parnas claimed he delivered the message, the US State Department announced that vice president Mike Pence would no longer be attending the inauguration of Ukrainian President Volodymir Zelenskiy.

Mr Parnas alleged that Mr Trump ordered Mr Pence to stay away at the behest of Mr Giuliani to send a clear message to the incoming Ukrainian administration that they needed to take seriously the demand for an investigation into Mr Biden, a Democratic presidential candidate seen as a potential threat to Mr Trump’s 2020 re-election.

Mr Parnas claimed that every communication he had with Mr Zelenskiy’s team was at the direction of Mr Giuliani, whom he regularly overheard briefing Mr Trump about their progress by phone.

“President Trump knew exactly what was going on,” said Mr Parnas, a Soviet-born Florida businessman facing a raft of criminal charges related to alleged campaign finance violations.

“He was aware of all my movements. I wouldn’t do anything without the consent of Rudy Giuliani, or the president.”

If true, Mr Parnas’s account undercuts a key Republican defence of Mr Trump deployed during the ongoing impeachment fight — that Mr Trump’s withholding of vital military aid to Ukraine last summer was not a quid pro quo for Biden investigations because Mr Zelenskiy did not know the money was being held up.

Trump impeachment
The US House of Representatives voted to send two articles of impeachment against Donald Trump to the Senate (Susan Walsh/AP)

Mr Giuliani called Mr Parnas’s statements “sad”.

“I feel sorry for him,” Mr Giuliani said. “I thought he was an honourable man. I was wrong.”

Asked directly if Mr Parnas was lying, Mr Trump’s lawyer replied: “I’m not responding yet.”

Mr Parnas claimed he also heard Mr Giuliani and another Trump-aligned defence lawyer, Victoria Toensing, briefing attorney general William Barr by phone about their efforts to pressure the Ukrainian government to announce the investigation into Mr Biden and his son Hunter’s business dealings.

“Barr was basically on the team,” Mr Parnas said.

The Justice Department said in September that Mr Trump had not spoken to Mr Barr about having Ukraine investigate the Bidens and that the attorney general had not discussed Ukraine with Mr Giuliani. Justice Department spokeswoman Kerri Kupec said on Wednesday that Mr Parnas’s claims were “100% false”.

The new accusations came as House Democrats made public a trove of documents, text messages and photos from Mr Parnas’s smartphones that appear to verify parts of his account.

A federal judge earlier this month ruled that Mr Parnas could provide the materials to Congress as part of the impeachment proceedings. Democrats voted in December to impeach Mr Trump for abuse of power and for obstruction of Congress.

A House committee chairman said on Wednesday his panel will investigate what he says are “profoundly alarming” text messages among the newly disclosed materials that have raised questions about the possible surveillance of former ambassador to Ukraine Marie Yovanovitch before she was ousted by the Trump administration last spring.

The messages show that a Robert F Hyde, a GOP candidate for Congress from Connecticut, disparaged Ms Yovanovitch in messages to Mr Parnas and gave him updates on her location and phone use.

Eliot Engel, a New York Democrat who chairs the House foreign affairs committee, said that the messages are “profoundly alarming” and “suggest a possible risk” to Ms Yovanovitch’s security in Kyiv before she was recalled from her post.

“These threats occurred at the same time that the two men were also discussing President Trump’s efforts, through Rudy Giuliani, to smear the ambassador’s reputation,” Mr Engel said.

He said the committee staff flagged the information for the State Department’s Bureau of Diplomatic Security and is seeking assurances that proper steps have been taken to ensure the security of Ms Yovanovitch and committee staff. He said he also wanted to know what, if anything, the State Department knew about the situation.

“This unprecedented threat to our diplomats must be thoroughly investigated and, if warranted, prosecuted to the fullest extent of the law,” Mr Engel said.