Ukraine announced on Thursday that it has opened an investigation into suggestions that former U.S. ambassador Marie Yovanovitch was under illegal surveillance before she was recalled from Kyiv by President Trump last May.

And the Ukrainian Interior Ministry has asked the FBI to help, the Associated Press reports.

“The national police has initiated the creation of a joint international investigation team, to which FBI representatives have already been invited by the ministry,” Reuters reports, quoting a Ukrainian official.

The announcement came two days after House Democrats “released a trove of documents that showed Lev Parnas, an associate of President Donald Trump’s personal lawyer [Rudy Giuliani], communicating about the removal of … Yovanovitch as the U.S. ambassador to Ukraine,” the AP says.

The documents “included several cryptic WhatsApp messages between Lev Parnas and [current Republican Congressional candidate] Robert Hyde that discussed monitoring Yovanovitch’s physical movements and electronic devices,” reports Buzzfeed, adding that:

“In the texts between the men, Hyde calls Yovanovitch a [crude name] and suggests he’s in touch with people in Ukraine who were actively watching the ambassador.”

Bringing the FBI into the investigation “was a remarkable departure from past practice for the new government of [Ukraine] President Volodymyr Zelensky, which has tried hard to avoid any hint of partisanship in its dealings with Washington,” says the New York Times.

A Ukrainian Interior Ministry official went out of his way to emphasize that his country has no wish to “interfere in the domestic affairs of the United States,” but said Ukraine “cannot ignore such illegal activities on its territory.” 

In an interview Wednesday on MSNBC, Parnas said Trump knew of the work he was doing for Giuliani in Ukraine.

“He [Trump] was aware of all my movements,” Parnas said. “I wouldn’t do anything without the consent of Rudy Giuliani or the president.” Parnas now faces U.S. charges of campaign finance violations.

In a separate, but directly connected, investigation, Ukraine said has also asked the FBI to help determine if Russian military hackers broke into computers of the Ukrainian gas company Burisma. Former vice president Joe Biden’s son, Hunter, formerly served on Burisma’s board.

Parnas was involved in a campaign led by Giuliani, the Times says, “to pressure the Ukrainian government” to investigate Joe Biden, a Democratic presidential candidate, and his son.

Trump’s subsequent phone call with Zelensky — pressing for a public announcement of a Biden investigation while withholding hundreds of millions of dollars in U.S. military aid for Ukraine — is at the center of the impeachment trial that opened in Washington on Thursday.