Yulia Tymoshenko has served as Ukraine’s prime minister in 2005 and from 2007 to 2010.

Ukraine’s former prime minister, Yulia Tymoshenko, has been accused of bribing members of the country’s parliament and running a vote-buying scheme, the National Anti-Corruption Bureau of Ukraine (NABU) said, according to media reports.

In a statement on the Telegram messaging application on Wednesday, NABU said it had served charges of bribery to an opposition party chief after exposing several other lawmakers last month as members of a “systemic” plot to receive payments in exchange for votes.

“This concerned not one-off arrangements, but a regular cooperation mechanism that envisaged advance payments and was designed for a long-term period,” NABU added.

A source familiar with the matter told the Reuters news agency that Tymoshenko was the subject of the probe.

A spokesperson for the Specialised Anti-Corruption Prosecutor’s Office (SAPO) also told Ukrainian media that Tymoshenko had been charged after SAPO and NABU officers raided her Batkivshchyna (Fatherland) political party’s offices.

Tymoshenko, who rose to prominence two decades ago as a leader of the pro-democratic Orange Revolution and served as Ukraine’s prime minister in 2005, and again from 2007 to 2010, has denied “all accusations” but didn’t specifically address the probe.

In a Facebook post, the opposition leader pledged to clear her name in court.

Her political influence in recent years has significantly diminished, with her Fatherland party holding approximately two dozen seats in Ukraine’s 450-seat legislature.

The probe into Tymoshenko broadens an anticorruption campaign in Ukraine that has ensnared senior ministers and opposition lawmakers.

But tackling corruption remains a crucial condition for Ukraine’s European Union membership bid, a goal Kyiv views as central to its post-war future.

NABU and anticorruption prosecutors shocked Ukrainians last November by unveiling an alleged $100m kickback scheme in the energy sector involving a former associate of President Volodymyr Zelenskyy.

Last July, the Ukrainian president had passed a bill which sought to curb the country’s anticorruption agencies’ independence.

But after November’s reports from NABU and following months of widespread protests against his controversial bill, Zelenskyy urged full cooperation with the investigation.

In a television address to the country last November, he had said that everyone in the country “who has been involved in corruption schemes must receive a clear legal response. There must be criminal verdicts”.