Clashes broke out between government forces and pro-Russian separatists in eastern Ukraine on Thursday, as Russia called for new talks to solve the crisis.
Up to five pro-Russian militants were killed during a raid in the eastern town of Sloviansk, the Ukrainian Interior Ministry said Thursday.
One government soldier was injured during the operation to disband three checkpoints, the ministry said.
Earlier, pro-Russian militia said that at least one man was killed and another severely wounded when gunmen attacked a checkpoint outside the town.
Video footage from the region showed armoured personnel carriers advancing over burning barricades.
Reporters say military helicopters were seen circling over Sloviansk, which has been the epicentre of a pro-Russian uprising in the region.
In the nearby town of Artemivsk, government troops fought off an attack on an army base.
One Ukrainian soldier was wounded while the attackers suffered “serious losses”, Ukrainian interim President Oleksandr Turchynov told Parliament.
The Ukrainian Defence Ministry said that the attackers, numbered around 100, were armed with automatic rifles and grenade launchers.
In the southern city of Mariupol pro-Russian protesters reportedly retook the city administration after a botched attempt by government forces to storm the building.
Reports also say that the Russian flag was back up on the administration’s roof and law enforcement agents were negotiating with the occupants.
Ukrainian Interior Minister Arsen Avakov said earlier that the building had been retaken in an operation carried out by “civilian activists”.
Pro-Russian militants have seized numerous buildings in the mainly Russian-speaking industrial region.
Russian Foreign Minister Sergei Lavrov said on Wednesday that all sides should sit down for more talks.
“The latest offer by the Russian President (Vladimir Putin) has been supported and I believe that it will materialise in practice soon,” Lavrov told students in Moscow.
The minister reiterated Moscow’s position that the West had aided the overthrow of Ukrainian president Viktor Yanukovych and is sponsoring the current western-leaning government in Kiev.
The EU and the U.S. accused Russia of backing the separatists in eastern Ukraine.
U.S. President Barack Obama warned of another round of sanctions against Russia.
“We have been consistently preparing for the prospect we are going to have to engage in further sanctions. Those are teed up,” Obama said during a visit to the Japanese capital Tokyo.