Three Ukrainians who aided the Donald Trump campaign's efforts to discredit the Biden family have been charged with treason.
The 2019 drive was led by former New York Mayor Rudy Giuliani, who was Mr Trump's personal lawyer at the time.
It centred on unproven allegations that Joe Biden had corrupt dealings with Ukraine as vice-president.
Ukraine's Security Service (SBU) said the three men charged were paid by Russian military intelligence (GRU).
It added that they had used a "tense political situation" to harm Ukraine's reputation abroad.
The three men charged are understood to be current MP Oleksandr Dubinsky, former lawmaker Andriy Derkach and ex-prosecutor Kostyantyn Kulyk.
Mr Dubinsky has denied the charges.
All three are said to be members of an agent network led by Russian Gen Vladimir Alekseyev, the deputy head of the GRU.
The charges allege they pursued "information subversive activities" related to the 2020 US election and were paid $10m (£8m).
The men are accused of helping to spread the falsehood that Ukraine, rather than Russia, interfered in the recent US elections.
The allegations against Mr Biden involved the business dealings of his son Hunter, who was a director of Ukrainian natural gas company Burisma.
Mr Trump and his allies suggested that Mr Biden, as Barack Obama's vice-president, encouraged the firing of Ukraine's top prosecutor, Viktor Shokin, because he had been investigating Burisma.
Hunter Biden has since filed a lawsuit against Mr Giuliani for "the total annihilation" of his privacy via the former New York mayor's search for damaging information related to the Biden family.
Ukrainian authorities did not explicitly identify Mr Dubinsky, instead using his alleged Russian intelligence call sign "Burtino".
However, the lawmaker identified himself in a Telegram post, saying that a court in Kyiv had ordered his detention for 60 days on the basis of the charges.
Mr Dubinsky denied all wrongdoing in a series of posts on Telegram and alleged that he faced political persecution directed at him by President Volodymyr Zelensky's office.
He faces 15 years in prison and the forfeiture of his assets if convicted.
Mr Derkach and Mr Kulyk fled Ukraine after Russia's invasion in 2022, the SBU said.
Mr Dubinsky, Mr Derkach and Mr Kulyk were previously sanctioned by the US government in the final days of Mr Trump's administration for their alleged efforts to undermine the 2020 election in the US.
The Treasury Department identified Mr Derkach as a Russian agent. He is named in the nearly 1,000-page report produced by the US Senate Intelligence Committee on Russia's interference in the 2016 US election.
Mr Derkach publicly met Mr Giuliani in Ukraine in 2019 as part of their effort to link Hunter Biden to corruption in Ukraine.
He also appeared with Mr Giuliani in right-wing US media ahead of the 2020 election, where they shared details of their alleged investigation.
Separately, while serving as a Ukrainian deputy prosecutor general, Mr Kulyk wrote a 2019 memo that pushed for Ukraine to investigate Hunter Biden's role on Burisma's board.
It included unsupported claims that he had evidence President Joe Biden unlawfully enriched himself, which reportedly sparked Mr Giuliani's search for incriminating information in Ukraine.
Mr Giuliani, like Mr Trump, faces numerous legal issues in the US related to his efforts to overturn the 2020 election results.
Mr Trump also pushed for Ukrainian lawmakers to investigate Hunter Biden, most famously in a phone call with President Zelensky.
Congressional Democrats impeached the former US president as he had withheld military aid for Ukraine while pressuring Mr Zelensky.
Mr Trump was later acquitted in the US Senate with Republican support.
