KIEV (Reuters) - Ukraine has asked the FBI in the United States for help investigating a suspected cyberattack by Russian military hackers on Burisma, an energy company caught up in the impeachment of U.S. President Donald Trump.

The Ukrainian interior ministry on Thursday also announced an investigation into the possible illegal surveillance of Marie Yovanovitch, formerly the American ambassador to Kiev, following the release of text messages this week by the U.S. Congress as part of the impeachment case.

The FBI said it had visited the home and business of Robert Hyde, a Republican congressional candidate in Connecticut who sent the text messages to Lev Parnas, an associate of Trump attorney Rudy Giuliani, that suggested Hyde had Yovanovitch under surveillance. The FBI declined to give further details.

Hyde was not immediately available for comment but on Twitter he has said he has never been to Kiev and that he made up the story about keeping watch on Yovanovitch to fool Parnas.

The FBI declined to comment on Ukraine’s request for help after California-based cybersecurity company Area 1 Security on Monday identified the hacking of Burisma Holdings and linked it to Russia’s Main Directorate of Military Intelligence, or GRU.

Burisma was at the center of attempts by Trump in July to persuade Ukraine to announce an investigation into Joe Biden, a Democratic presidential contender, and his son, Hunter, who used to have a seat on the Ukrainian company’s board.

There has been no evidence of wrongdoing by the Bidens, who reject Trump’s allegations of corruption.

Trump’s efforts have led to him being impeached on charges of abuse of power and obstruction of Congress. The president, who denies wrongdoing, faces a trial in the U.S. Senate next week.

The same hacking group, known as “Fancy Bear” or “APT28” by cybersecurity researchers, breached the Democratic National Committee in 2016 in what U.S. investigators described as part of an operation to disrupt that year’s election.

Russia’s defence ministry did not respond to a request for comment about Area 1 Security’s assertions.

“It is noted that the hacking attack was probably committed by the Russian special services,” Ukrainian interior ministry official Artem Minyailo said at a briefing.

Minyailo said Ukraine had asked the FBI and Area 1 Security for assistance regarding information that hackers stole personal employee data and emails from executives at Burisma and other companies. These other companies included the media production company of President Volodymyr Zelenskiy, he said.

“The national police has initiated the creation of a joint international investigation team, to which FBI representatives have already been invited by the ministry,” Minyailo said.

A view shows a building, which reportedly houses an office of a subsidiary of the Ukrainian energy company Burisma Holdings Ltd, in Kiev, Ukraine January 14, 2020. REUTERS/Valentyn Ogirenko

YOVANOVITCH SURVEILLANCE PROBE

It was not clear what data the hackers wanted to steal, Area 1 said. Breaching Burisma could yield communications from, to or about Hunter Biden, who served as a director between 2014 and 2019.

A source close to Burisma told Reuters earlier this week the company’s website had been subject to multiple break-in attempts over the past six months but did not provide further details.

Ukrainian officials said they were also probing allegations that Yovanovitch, the former ambassador to Ukraine, was subject to illegal surveillance before Trump fired her in May.

U.S. Senator Robert Menendez, the top Democrat on the Senate Foreign Relations Committee, told CNN on Thursday he had sent a letter to the State Department seeking an immediate briefing.

A former senior security official with the U.S. State Department told Reuters he did not regard the Hyde text messages as constituting an actual threat to Yovanovitch.

“I would have trouble going to a U.S. Attorney and saying, ‘I want an arrest warrant for this person or I want to open an investigation,’” said the former senior security official, who spoke on condition that he not be identified.

“I might send somebody to talk with them and say, you know, ‘You have any intent to harm her?’ and if he says no and there’s no other evidence to the contrary ... that’s probably as far as I would go.”