President Volodymyr Zelenskyy's powerful chief of staff and top negotiator, Andriy Yermak, resigned on Friday shortly after Ukraine's anti-corruption authorities raided his home.
Investigators earlier this month said they had uncovered a $100-million kickback scheme in the strategic energy sector, triggering widespread public anger at a time when Russia is hammering Ukraine's power grid, causing blackouts and threatening winter heating outages.
The resignation and raids are another blow to Mr Zelenskyy, who is facing a mounting Russian offensive in the east just as the United States, a crucial ally, tabled a surprise plan to end the war that heavily favoured Moscow.
"The Office of the President of Ukraine will be reorganised. The head of the office, Andriy Yermak, has submitted his resignation," Zelensky said in a video address, adding he would hold consultations with a possible replacement on Saturday.
Mr Yermak, 54, was named Ukraine's top negotiator in talks with Washington to refine that proposal, and analysts said the raids could hurt Kyiv's position.
Early Friday, the National Anti-Corruption Agency (NABU) said it, along with the Specialised Anti-Corruption Prosecutor's Office (SAP), were "conducting investigative actions (searches) at the head of the Office of the President of Ukraine."
It did not say what the investigation was about.
Mr Yermak said he was cooperating.
"There are no obstacles for the investigators. They have been given full access to the apartment, and my lawyers are present on-site, cooperating with the law enforcement officers. From my side, there is full cooperation," he said on social media.
'Influence'
Mr Yermak is Mr Zelenskyy's most important ally, but a divisive figure in Kyiv, where his opponents say he has accumulated power, gate-keeps access to the president and ruthlessly sidelines critical voices.
A former film producer and copyright lawyer, Mr Yermak came into politics with Mr Zelenskyy in 2019, previously working with him during the now-president's time as a popular comedian.
Mr Yermak is widely considered the second-most influential man in the country and even sometimes nicknamed "vice-president".
Opposition figures have alleged Mr Yermak is connected to the massive corruption scandal that has engulfed Kyiv.
Mr Zelenskyy sacked two ministers over the scandal, and one of his close friends and business associates, Timur Mindich, was accused of masterminding the scheme.
Speaking after the raid on Mr Yermak was announced, the European Union backed the work of Ukraine's anti-corruption agencies.
"We have a lot of respect for those investigations which show that the anti-corruption bodies in Ukraine are doing their work," said European Commission spokeswoman Paula Pinho.
