Image copyright Reuters Image caption Ukrainian-American businessman Lev Parnas is an associate of President Trump's personal lawyer

An aide to Donald Trump's lawyer claims the president "knew exactly what was going on" with efforts to pressure Ukraine into investigating former Vice-President Joe Biden and his son.

Lev Parnas told MSNBC he went to Ukraine to put pressure on officials on behalf of Mr Trump and his personal lawyer, Rudy Giuliani.

The alleged intention was to damage Mr Biden, a potential Democratic rival to Mr Trump in this year's US election.

President Trump denies involvement.

The US president also says that he does not know Mr Parnas - a Ukrainian-American businessman and Republican party donor who is facing separate charges of campaign finance violations.

The extent of Mr Trump's involvement in the alleged plan to undermine Mr Biden - whose son Hunter Biden was on the board of Ukrainian gas firm Burisma - will be examined in his impeachment trial, which is due to begin next week in the US Senate.

He is accused of abuse of power and obstruction of Congress.

What did Lev Parnas say?

In the interview aired on Wednesday, Mr Parnas said Mr Trump was "aware of all my movements".

"I wouldn't do anything without the consent of Rudy Giuliani or the president. Why would [Ukrainian] President Zelensky's inner circle or [Interior] Minister [Arsen] Avakov or all these people or [former] President [Petro] Poroshenko meet with me?

"Who am I? They were told to meet with me. And that's the secret that they're trying to keep. I was on the ground doing their work," he added.

Image copyright AFP Image caption Rudy Giuliani has been central in pushing the suggestion that the Bidens were involved in wrongdoing in Ukraine

Mr Trump "decided to" increase pressure on Ukraine to investigate the Bidens' activities by withholding military aid, Mr Parnas said.

Mr Parnas also said he told a Ukrainian official that US Vice-President Mike Pence would not attend President Zelensky's inauguration unless there was an investigation into the Bidens.

Other White House officials knew about the alleged campaign against Mr Biden, Mr Parnas alleged. They included Attorney General William Barr, who Mr Parnas said was "basically on the team", and former national security advisor John Bolton, who Mr Parnas said "100%" knew about it.

Mr Trump has said he does not know Mr Parnas. Referring to photos of himself with Mr Parnas and another Giuliani associate, he said: "It's possible I have a picture with them because I have a picture with everybody."

But Mr Parnas said Mr Trump "lied". "He knew exactly who I was." he said.

What else has Parnas provided?

Earlier this week, letters, phone records, notes and flash drives were obtained from Mr Parnas in a bid to bolster the Democrats' case against Mr Trump at the forthcoming Senate trial.

Documents show that Ukraine-born Mr Parnas was in regular contact with Mr Giuliani as well as Ukrainian officials, and suggest that Mr Parnas was directly involved in trying to have Mr Zelensky look into Mr Biden.

One handwritten note from Mr Parnas states: "Get Zalensky [sic] to Annonce [sic] that the Biden case will be investigated."

There is also a screenshot of a previously undisclosed letter from Mr Giuliani to Mr Zelensky, in which he asks to arrange a meeting.

Image copyright House Intelligence Committee

The letter from Mr Giuliani describes himself as "personal counsel to President Trump" and states that Mr Trump had "knowledge and consent" of Mr Giuliani's actions.

The meeting never took place, as Mr Giuliani eventually cancelled his May trip to Ukraine.

What about the former US ambassador to Ukraine?

Some of the materials obtained show Mr Parnas and Mr Giuliani discussing the removal of Marie Yovanovitch, the then US ambassador to Ukraine.

Several of the text messages appear to suggest Ms Yovanovitch was placed under surveillance.

In Wednesday's interview, Mr Parnas claimed the only motivation to have Ms Yovanovitch removed was because she was in the way of the effort to get Ukraine to announce an investigation into Joe Biden.

Mr Parnas was apparently given updates on the ambassador's location and mobile phone use by a man named Robert F Hyde.

Mr Hyde is a Republican congressional candidate in Connecticut and a Trump campaign donor.

Ms Yovanovitch is calling for an investigation into the messages.

"The notion that American citizens and others were monitoring [her] movements... is disturbing," her lawyer said.

On Thursday, Ukraine announced a criminal investigation into the possible illegal collection of information about the former ambassador.

Media playback is unsupported on your device Media caption A beginner's guide to impeachment and Trump

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