Washington — Authorities in Ukraine have launched a criminal investigation into whether former U.S. Ambassador to Ukraine Marie Yovanovitch was illegally monitored while she was serving in Kiev, the country's Ministry of Internal Affairs announced Thursday.

The criminal probe stems from newly revealed messages exchanged between Lev Parnas, an associate of Rudy Giuliani, and Robert Hyde, a Republican donor and congressional candidate from Connecticut, which show the two seemingly discussing Yovanovitch's whereabouts. Hyde has said the messages were made in jest and did not represent an actual effort to track Yovanovitch's movements.

Parnas aided Giuliani, Mr. Trump's personal attorney, with his efforts to pressure Ukraine to announce investigations targeting former Vice President Joe Biden and his son Hunter. Parnas and another associate of Giuliani's were indicted in October on federal campaign finance charges. Parnas turned over a trove of messages and other documents to the House Intelligence Committee, which has been among the committees leading the impeachment efforts against President Trump.

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"Our goal is to investigate whether there actually was a violation of Ukrainian and international law, which could be the subject for proper reaction, or whether it is just bravado and fake information in the informal conversation between two U.S. citizens," the Ministry of Internal Affairs said in a statement.

The ministry said it is Ukraine's position "not to interfere in the domestic affairs" of the U.S., but the messages exchanged between Hyde and Parnas "contain a possible violation" of Ukrainian law and the Vienna Convention on Diplomatic Relations, which governs the rights of diplomats in foreign countries.

"Ukraine cannot ignore such illegal activity on the territory of its own state," the Ministry said.

In the messages from March made public by House Democrats on Tuesday, Hyde told Parnas that Yovanovitch was "under heavy protection outside Kiev."

"They are moving her tomorrow," Hyde said in a subsequent message. "She's talked to three people. Her phone is off. Computer is off."

In another exchange, Hyde called Yovanovitch a "political puppet."

"If you want her out they need to make contact with security forces," he wrote to Parnas.

Yovanovitch, who was the subject of a smear campaign orchestrated by Giuliani and his associates, was abruptly recalled from her post in May due to concerns about her safety, she told lawmakers in November.

Giuliani told CBS News he was unaware of apparent efforts to surveil Yovanovitch. Hyde said he was "absolutely not" tracking the former ambassador.

"We just sent some colorful texts, you know, had a few pops, say, back when I used to drink," Hyde told Eric Bolling in an interview on his Facebook show "America This Week."

Parnas also said he did not believe Yovanovitch was in danger and assumed Hyde was drunk when he sent the messages.

But Lawrence Robbins, an attorney for Yovanovitch, called the notion that she was being monitored for unknown reasons "disturbing" and called for an investigation.

In addition to the probe launched by Ukrainian authorities, House Foreign Affairs Committee Chairman Eliot Engel demanded the State Department turn over information about the "unprecedented threat" to Yovanovitch and announced his panel would be opening an investigation.