Italy has expelled 30 Russian diplomats because of security concerns, it quotes a spokesman for Foreign Minister Luigi Di Maio as saying.

And it says Denmark has expelled 15 of Russia's diplomats following emerging evidence of civilian killings in the Ukrainian town of Bucha, near Kyiv.

Sweden also says it will expel three Russian diplomats who aren't acting in line with the Vienna Convention's international rules, foreign minister Ann Linde is reported as saying.

Russia's former president and deputy security council chairman Dmitry Medvedev has responded by saying it will retaliate and "slam shut the door on Western embassies", Reuters adds.