Story highlights Separatists fired artillery toward Mariinka, Ukrainian general command media office says

It says 200 separatists attacked Ukrainian positions, denies reports that 25 Ukrainian soldiers were wounded

Clashes began because of "provocations" by Ukrainian forces, separatist spokesman says

(CNN) Heavy artillery fire was reported Wednesday around the city of Donetsk in eastern Ukraine in what observers described as some of the worst fighting in the months since a shaky ceasefire was declared.

Separatists fired heavy artillery from Donetsk toward Mariinka early Wednesday, the Ukrainian general command media office said. Controlled by Ukrainian government forces, Mariinka sits on a strategically vital highway to the west, where checkpoints mark the end of separatist-controlled territory.

The general command said 200 separatist militants attacked Ukrainian positions, with an exchange of fire for six hours. It denied reports that 25 Ukrainian soldiers were wounded or that their positions were surrounded.

Eduard Basurin, a spokesman for the separatist Donetsk People's Republic, confirmed the clashes in Mariinka, saying the fighting began because of "provocations" by Ukrainian forces. He added that Ukrainian forces shelled the city of Donetsk's Petrovsky and Kirovsky districts overnight. Separatists hold Donetsk.

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Vladimir Kononov, the self-declared defense minister for the Donetsk People's Republic, told a news agency working with the separatists that their forces could not have stormed the Ukrainian controlled-Mariinka because they have always had a presence there.

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