KIEV (Reuters) - Ukraine plans to fire the prosecutor who led investigations into the firm where Joe Biden’s son served on the board, a central figure in the activity at the heart of impeachment proceedings against U.S. President Donald Trump, a source told Reuters.

Deputy Head of the Department of International Legal Cooperation of the Prosecutor General’s Office of Ukraine Kostiantyn Kulyk attends a news conference in Kiev, Ukraine April 11, 2019. REUTERS/Viacheslav Ratynskyi

Trump’s personal lawyer Rudy Giuliani has acknowledged meeting the prosecutor, Kostiantyn Kulyk, to discuss accusations against the Bidens.

The decision to sideline someone who played an important role in Giuliani’s efforts to find out damaging information about the Bidens comes as Ukraine has tried to avoid getting drawn into a partisan fight in Washington.

Trump’s Democratic opponents have launched impeachment proceedings, arguing that Trump abused his power by pressing Ukraine to investigate the Bidens to hurt the former vice president, front-runner to challenge him in the 2020 election.

The source said a decision had been taken to fire Kulyk for failing to show up for an exam that all employees of the General Prosecutor’s Office have been ordered to pass to keep their jobs during a clean-up of the prosecution service.

Prosecutor General Ruslan Ryaboshapka has already fired more than 400 prosecutors, or around a third of all staff.

Some prosecutors have told Reuters that many of those sacked had refused to sit the exam in protest at what they see as a purge designed to cement new President Volodymyr Zelenskiy’s political control of the service.

Zelenskiy has said the overhaul is essential because the office is widely distrusted by Ukrainians and had been seen as a political tool for the well-connected to punish their enemies.

Trump discussed investigating the Bidens during a July 25 phone call with Zelenskiy. Trump’s Democratic opponents have launched impeachment proceedings, arguing that Trump abused power to press Ukraine to hurt a political foe. Trump calls the investigation a witch hunt and denies wrongdoing.

Reuters was unable to reach Kulyk for comment. He was not present at a home address where Reuters has spoken to him in the past.

Kulyk did not show up for the mandatory exam, which was imposed last month, the source said.

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He also did not file an official justification for missing it, as other prosecutors have done, and will consequently be dismissed, the source said. His dismissal will take place by Dec. 31, if not earlier.

Earlier this year, Kulyk compiled a seven-page dossier on the business activities of Hunter Biden in Ukraine, two sources told Reuters.

Reuters could not independently verify the existence of such a dossier but Kulyk detailed his investigations into areas of interest to Trump and Giuliani in an interview with a pro-Trump columnist for The Hill newspaper in April.

Kulyk has been responsible for formally investigating a criminal case related to the founder of Ukrainian energy company Burisma. Biden’s son sat on the company’s board from 2014-2019.

In a recent interview, Giuliani told Reuters he met Kulyk in Paris. He said at that meeting Kulyk echoed allegations that in 2016 Biden had tried to have Ukraine’s then-chief prosecutor, Viktor Shokin, fired to stop him investigating Burisma. Biden has accused Giuliani of peddling “false, debunked conspiracy theories” for repeating these allegations.

“(Kulyk) was another prosecutor somewhat lower level who told me the same thing: that there was collusion and Biden had (the) prosecutor fired to kill case on (his) son and Burisma,” Giuliani told Reuters.

Giuliani did not respond to a request for comment on the decision to fire Kulyk. A spokesman for Joe Biden declined comment.

Kulyk told Reuters in October that he had been investigating Burisma’s founder, Mykola Zlochevsky, for around two years.

Reuters could not independently verify the extent of Kulyk’s involvement, but a source close to the energy company saw a spike in activity by Kulyk in regards to Burisma after Giuliani’s interest in the company and the Bidens had been conveyed to Kulyk’s then superior, Lutsenko.

In late January, Kulyk sent Zlochevsky the first of several summons for questioning, documents seen by Reuters showed.

Zlochevsky has not commented on the summons or an announcement by Ryaboshapka in October that his office was reviewing a series of investigations linked to Zlochevsky.

In April, Kulyk gave an interview to the columnist John Solomon at The Hill newspaper in Washington. In that article, Kulyk said he and other prosecutors were investigating allegations concerning Shokin’s dismissal.

Kulyk told The Hill that Ukrainian officials had unsuccessfully tried to pass on evidence on this and other probes to the U.S. authorities before looking for other people, including Giuliani, to present their findings.