Democrats in the United States have released a trove of documents obtained from Lev Parnas, a close associate of President Donald Trump's personal lawyer Rudy Giuliani, including a handwritten note that mentions asking Ukraine's president to investigate "the Biden case".

The documents, obtained as part of the impeachment investigation into the president, show Parnas communicating with Giuliani and another attorney before the removal of Marie Yovanovitch, who was the US ambassador to Ukraine.

More:

A man named Robert F Hyde disparaged Yovanovitch in messages to Parnas and gave him updates on her location and mobile phone use, raising questions about possible surveillance.

Democrats released the files on Tuesday as they prepared to send articles of impeachment to the Senate for Trump's trial. The documents add new context to their charges that Trump pressured Ukraine to investigate Democrats as he withheld military aid.

Parnas was in frequent communication with Giuliani and with Ukrainian officials, the messages show. He appeared to be pushing unsubstantiated allegations that Democrat Joe Biden and his son, Hunter Biden, were somehow engaged in corruption in Ukraine.

Among the documents is a screenshot of a previously undisclosed letter from Giuliani to Ukrainian President Volodymyr Zelenskyy dated May 10, 2019, which was before Zelenskyy took office.

In the letter, Giuliani requests a meeting with Zelenskyy "as personal counsel to President Trump and with his knowledge and consent".

Watching ambassador

One of the documents is a handwritten note on stationery from the Ritz-Carlton Hotel in Vienna that says: "get Zalensky to Annonce that the Biden case will be Investigated."

Trump asked Zelenskyy in a July call to investigate Biden - his political rival - and his son Hunter. Hunter Biden served on the board of a gas company based in Ukraine.

Democrats said that Parnas's lawyer confirmed that Parnas wrote the notes.

The documents - including phone records, texts and flash drives turned over by Parnas - were sent to the House Judiciary Committee by three other House panels "to be included as part of the official record that will be transmitted to the Senate along with the Articles of Impeachment," according to a statement.

Former US Ambassador to Ukraine Marie Yovanovitch gave evidence before the House Intelligence Committee inquiry. New documents include communications about her removal from office [File: J. Scott Applewhite/AP Photo]

Some of the materials were made public while others were marked as sensitive.

Parnas and his business partner, Igor Fruman, both US citizens who emigrated from the former Soviet bloc, were indicted last year on charges of conspiracy, making false statements and falsification of records.

Prosecutors allege they made outsize campaign donations to Republican causes after receiving millions of dollars originating from Russia.

In several of the documents, Parnas communicated with Giuliani and another lawyer, Victoria Toensing, about the removal of Yovanovitch. The ambassador's removal, ordered by Trump, was at the centre of the Democrats's impeachment inquiry. Yovanovitch testified in the House impeachment hearings that she was the victim of a "smear campaign".

Trump on a July 25 call had promised Zelenskyy that Yovanovitch was "going to go through some things". Roughly two months earlier, she was recalled from her diplomatic post.

On April 23, the day before Yovanovitch was directed to return to the US, Giuliani texted Parnas, "He fired her again." Parnas texted back, "I pray it happens this time I'll call you tomorrow my brother."

Parnas also received messages from Hyde, who referred to Yovanovitch as a "b****." Hyde is now running for a US House seat in Connecticut.

The latest documents were obtained from Lev Parnas, a close associate of Trump's personal lawyer Rudy Giuliani, and reveal communications over Ukraine [File: Andrew Harnik/AP Photo]

After texting about the ambassador, Hyde gave Parnas detailed updates that suggested he was watching her. In one text, Hyde wrote: "She's talked to three people. Her phone is off. Her computer is off." He said she was under heavy security and "we have a person inside".

'Disturbing'

Hyde at one point texted Parnas that "they are willing to help if we/you would like a price," and "guess you can do anything in Ukraine with money ... is what I was told."

Parnas texted back: "lol."

Lawrence Robbins, a lawyer for Yovanovitch, called for an investigation into the messages.

"Needless to say, the notion that American citizens and others were monitoring Ambassador Yovanovitch's movements for unknown purposes is disturbing. We trust that the appropriate authorities will conduct an investigation to determine what happened."

Hyde could not immediately be reached and did not respond to requests for comment.

The text messages show that Parnas consulted Giuliani in January 2019 after the US denied a visa for former Ukrainian Prosecutor General Viktor Shokin. Giuliani replied: "I can revive it."

The following day, Giuliani told Parnas: "It's going to work I have no 1 in it." Giuliani then predicted "he will get one" before giving Parnas the phone number for Jay Sekulow, the leader of the president's personal legal team. Sekulow is expected to be one of Trump's lawyers during the impeachment trial.

A federal judge earlier this month ruled that Parnas could provide the materials to Congress as part of the impeachment proceedings.

Democrats voted in December to impeach Trump for abuse of power and for obstruction of Congress.