Ukraine said Thursday it had launched an investigation into alleged illegal surveillance of former US ambassador Marie Yovanovitch, who is now a key figure in President Donald Trump's impeachment inquiry.
Trump has denied accusations that he pressured Ukrainian officials to investigate political rival Joe Biden, part of the impeachment inquiry that threatens the US leader with removal from office.
Ukraine said it decided to act after fresh documents were released by US Democrats on Tuesday detailing the controversial removal of Yovanovitch, who served as the US ambassador to Ukraine for nearly three years before she was abruptly called back to the United States in May.
The newly-acquired files showed Trump's personal lawyer Rudy Giuliani working with Ukrainian-born American Lev Parnas last year to pressure Kiev to investigate Biden.
They also showed Giuliani and Parnas, working with Ukrainian officials, trying to force out Yovanovitch, who was eventually removed by Trump.
The files reportedly detailed exchanges in which Yovanovitch's location was discussed, indicating she may have been under surveillance.
The Ukrainian interior ministry said on Thursday it could not ignore "illegal activities" on its territory.
"Ukraine's position is not to interfere in the domestic affairs of the United States of America," the ministry said in a statement.
"However, the published references cited by the Washington Post contain a possible violation of the law of Ukraine and the Vienna Convention on Diplomatic Relations, which protects the rights of a diplomat on the territory of the foreign country," it said.
"Our goal is to investigate whether there actually was a violation of Ukrainian and international law," the ministry added.
"Or whether it is just a bravado and fake information in the informal conversation between two US citizens," it added in the English-language statement.
During Yovanovitch's testimony to Congress in November, the 33-year diplomatic veteran said she was subjected to a smear campaign orchestrated in part by Giuliani.
The interior ministry said it has also launched an investigation into a hacking attack against the website of Burisma Holdings, an energy company at the centre of the scandal that led to Trump's impeachment trial.
On Tuesday, California cyber firm Area 1 Security said Russia's GRU military intelligence launched a "phishing" campaign in November to access emails of Burisma employees.
Trump has been accused of pressuring Ukraine to investigate Burisma and its links to former board member Hunter Biden, the son of former vice president Joe Biden.
"The national police is initiating the creation of a joint international investigation team, to which FBI representatives will be invited," the interior ministry said.