Rudy Giuliani, personal lawyer for US President Donald Trump, left two unsolicited voicemails in a reporter phone, NBC News
In the reports, Mr Giuliani spoke about needing money and attacked Democratic presidential candidate Joe Biden.
Mr Giuliani has not yet commented on the calls.
Deputies requested documents from Mr Giuliani earlier this month as part of an investigation into the presidential impeachment.
In the past, he publicly admitted that he had asked Ukrainian officials to investigate widespread corruption allegations against Mr Biden.
- Trump's assistant aide called "Giuliani a hand grenade"
- Who's who Trump is signaling
Three Democratic-led committees are currently investigating whether President Trump has tried to pressure the Ukrainian president to investigate Mr Biden in return for the militia
What did Giuliani say?
NBC Investigative Reporter Rich Shapiro says he received two voicemails from Mr. Giuliani within one month.
He describes them as the result of "what is known, in casual speech, as a dial."
Mr. Shapiro missed the first conversation in the middle of the afternoon on September 28, since he was at a child's birthday party. He had interviewed Mr Giuliani for the article the previous day.
For the entire subsequent three-minute voicemail, the President's personal lawyer reportedly assaulted Mr. Biden and his family.
"Biden trades in a public office since he is a senator," Mr Giuliani told an unidentified man. In the conversation, he raised the discredited allegations that Joe Biden, when the vice president, stopped investigating Ukraine to protect his son, Hunter.
- What did Trump's lawyer do in Ukraine?
- The story of Trump's impeachment explained
"He did the same in China. And he tried to do it in Kazakhstan and Russia," Mr. Giuliani adds.
In a second voicemail left on the night of October 1
"We need several hundred thousand," Mr. Giuliani said at one point in a conversation that Mr. Shapiro said involved a Bahrain man and an unknown man named Robert.
Who is Rudy Giuliani?
Mr. Giuliani was a Major of New York from 1994 to 2001 and held the post during the September 11 terrorist attacks.
He was one of the candidates for the Republican nomination for president in 2008, before stepping down and supporting the eventual candidate, John McCain.
Since April 2018, he has been President Trump's lawyer.
Mr Giuliani was present during Mr Trump's call to Ukrainian President Vladimir Zelensky in July, which is the subject of an impeachment investigation.
His own activities in Ukraine are also under investigation.