Sustained gunfire was heard throughout the night near the eastern Ukrainian city of Slovyansk, the stronghold of pro-Russia fighters, ahead of a second round of European-brokered talks today aimed at resolving the crisis.
The Russian Foreign Ministry issued a statement condemning what it described as a sharp escalation in the violence in eastern Ukraine, accusing the Ukrainian government of using the talks as cover for military operations against its citizens.
The fighting began when forces loyal to the Kiev government moved in to protect a television tower near the small village of Andriyivka. Residents said it went on through the night.
Debris from the shooting was visible this morning, including a badly damaged train and craters caused by mortar bombs or other heavy artillery.
The Russian Foreign Ministry said some people were wounded, but gave no specifics.
Government forces in recent weeks have achieved only limited results in quashing the pro-Russia groups that have declared independence for Ukraine's eastern Donetsk and Luhansk regions.
Polls have shown, however, that a majority of eastern Ukrainians support a united country, although most are too fearful of the armed separatists to say so publicly.
In one south-eastern city, Mariupol, steelworkers retook government buildings from pro-Russia fighters and cleared away their barricades. Mariupol is a major industrial city in the Donetsk region, lying on the main road between Russia and the Crimean Peninsula, which Russia annexed in March.
And in the eastern village of Velyka Novosilka, armed backers of Ukrainian unity dressed in black seized control of a police station and vowed to expel the separatists in Donetsk through force if necessary.
Other similar and apparently unaccountable groups look to be emerging elsewhere in the chaotic east. Should they make substantial incursions, it is unclear whether they will be perceived as liberators or attackers working for the little-liked central government in Kiev. The latter could precipitate civil conflict.
The first round of talks on Ukraine's future was held on Wednesday in Kiev, but brought few visible results since those who declared independence in the east were not invited.
The second round was under way today in Kharkiv, an eastern city but one that has not seen major insurgent activity.
Russia has pushed for Ukraine to give more power to its regions, since that would allow Moscow to retain influence over areas in Ukraine dominated by Russian-speakers.
Many in western Ukraine, including in the capital, favour closer ties to Europe and fear being pulled back into Moscow's orbit.