Ukrainian authorities declared curfew on Sunday after three pro-Russia activists and one attacker were killed in a gun battle near the volatile eastern Ukrainian town of Slavyansk earlier in the day.

Ukrainian authorities declared curfew on Sunday after three pro-Russia activists and one attacker were killed in a gun battle near the volatile eastern Ukrainian town of Slavyansk earlier in the day.

"Four cars pulled up to our roadblock around 1:00am (1000 GMT Saturday). We wanted to conduct a check, and then they opened fire on us with automatic weapons," an eyewitness told journalists.

The man, who gave his name as Vladimir, said there were around 20 attackers, but he was not sure of casualties on their side.

Three of his fellow pro-Russia activists at the barricade were killed and four were wounded, he said.

"Reinforcements quickly arrived at our roadblock and the attackers left."

The identity of the attackers in Sunday's firefight was not given, but the separatist gunmen maintain a firm grip over a string of towns across Ukraine's industrial east despite an international deal demanding they vacate state buildings they are occupying.

The Western-backed authorities in Kiev had declared an Easter truce in their so far unsuccessful military operations to try to oust the separatists.

Last Thursday, three pro-Russian separatists were killed by Ukrainian troops when a mob of around 300 people tried to attack a military post in the southeast port city of Mariupol using Molotov cocktails and guns.