A Ukrainian officer has been killed in a gun battle with pro-Russian armed men in the eastern city of Sloviansk, the interior minister says.
Both sides suffered a number of casualties, Arsen Avakov said.
Pro-Russian forces took over Sloviansk on Saturday and have targeted at least four other cities, prompting Kiev to launch an “anti-terror operation”.
Kiev and Western powers accuse Moscow of inciting the trouble. The Kremlin denies the charge.