Politicians in Ukraine say impeachment proceedings have been launched against President Petro Poroshenko following a media expose linking him to a corruption scandal that involves Russia.

Former Ukrainian prime minister Yulia Tymoshenko, who is a frontrunner for next month's presidential election, made the announcement in Ukraine's parliament, the Verkhovna Rada, on Tuesday, saying the president had committed "high treason."

"An investigation by journalists about the president's corruption during [Ukraine's] war is the basis for initiating the procedure for state treason," Tymoshenko told reporters outside the Rada.

"We will start collecting signatures. My signature for Poroshenko's impeachment is the first."

The investigation

Tymoshenko's move was triggered by an expose released on Monday by BIHUS.info, a Ukrainian investigative organisation focused on anti-corruption, which linked Poroshenko to a money laundering and smuggling scandal involving Ukrainian officials and Russia.

The report, which can be viewed with English subtitles below, says high-level Ukrainian defence officials received "kickbacks" for smuggling spare parts of military equipment from Russia at inflated prices.

BIHUS.info journalists said they believed the scandal took place in 2015, amid the war between Ukraine and Russian-backed separatists in the country's east, and just a year after the Crimean Peninsula was annexed by Russia.

The report specifically focuses on Oleh Hladkovskyi, the first deputy secretary of Ukraine's National Security Council and close friend of Poroshenko.

It also focuses on Hladkovskyi's son and Ukrainian defence company UkrOboronPro, which was said to know the origin of the smuggled military parts.

According to the National Security Council, Hladkovskyi was suspended from his post on Tuesday afternoon, pending an investigation into the claims.

Hladkovskyi said he "categorically rejects all allegations made in the so-called investigation," in a statement released on Tuesday.

"In the investigation, as in most materials of this genre, it contains references exclusively to anonymous sources, it consists of a compilation of well-known facts and dirty fakes," he said.

"But since it caused a significant social resonance, we are all interested in putting points on the "i" and protecting the reputation of people who, in an extremely critical situation in 2014-2015, resolved urgent, vital and critical issues for restoring combat readiness of the army."

UkrOboronPro said in a statement that BIHUS.info journalists "manipulatively used closed information from criminal investigations," saying information referring to national security issues "must be obtained by a proper legal assessment of the competent authorities."

"The management of the company is concerned that all proceedings should be investigated as soon as possible, and officials involved in abuses were punished in accordance with the Law," the statement said.

Presidential election

This expose has not come at a good time for Poroshenko, who is already trailing in the polls for next month's presidential election.

A poll conducted in early February found that no presidential candidate was particularly liked, which is not uncommon in the country known for its cyncism directed toward politicians.

However, among the three frontrunners, a comedian, Volodymyr Zelensky, had edged to the lead spot in the race.

Poroshenko followed in second place in the same poll, while Tymoshenko came third.

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