Ukrainian President Volodymyr Zelensky signed a decree on Tuesday offering citizenship to Russian political refugees, and to foreigners who fought on Kiev's side in the conflict in eastern Ukraine.

Zelensky announced such a move last month in response to a Russian decree expanding the number of Ukrainians who can apply for fast-track Russian passports.

Separately Ukraine's state security service declared a Russian consular officer in the western city of Lviv as persona non grata, accusing him of spying. The officer had already left the country, a statement said.

Russia's Foreign Ministry said Moscow had expelled a Ukrainian consular worker from St. Petersburg in response, TASS news agency reported.

Ties between Kiev and Moscow have seen a dramatic twist after Zelensky invited Russian President Vladimir Putin to resume peace talks to solve the ongoing conflict between their respective countries last month.

Zelensky, who has said resolving ongoing disputes with Russia would be his top priority,called for internationally mediated talks via YouTube, saying "I suggest the following lineup for talks: me, you, U.S. President Donald Trump, British Prime Minister Theresa May, German Chancellor Angela Merkel, and French President Emmanuel Macron."

He also addressed the topic of the meeting, saying "Let's discuss who Crimea belongs to and who isn't in the Donbass region."

In response to the Ukrainian initiative, Kremlin spokesperson Dmitry Peskov called the proposal an "absolutely new format," saying the proposal would be reviewed.

Putin said that Moscow is ready for "any kind of talks" on the Ukrainian issue, including the expansion of the Normandy process. But he also emphasized it would only be possible after sufficient preparation as well as a well-formed government and a parliamentary election in Kiev.

Two days after the proposal, the two presidents had a telephone conversation during which they discussed issues of a settlement in the southeast of Ukraine and cooperation in returning detainees from both sides. They both agreed to continue their work at the expert level, according to a Kremlin statement.

The telephone conversation was Putin's first-ever contact with Zelensky after the latter was sworn in as Ukraine's president on May 20.

(With input from Reuters and Xinhua)