Military spokesman Olexesiy Zyuganov also said two more people were wounded in the clashes between Friday and Saturday evening. He accused the "Russian occupying forces" of breaching the truce nine times, with three of the incidents involving weapons banned by the Minsk agreement.
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Separatist forces reportedly used grenade launchers, large-caliber machine guns and a sniper during a clash near the rebel-controlled city of Luhansk.
"Unfortunately, during the course of the battle, two of our soldiers sustained deadly injuries," Zyuganov said.
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A separate clash claimed two lives when one soldier was fatally wounded and another who tried to help him was also killed, Battalion commander Babanin Volodymyr said at the briefing.
"Both servicemen died as heroes and will forever stay in our hearts," he added.
Donbass vote 'at gunpoint of Russian guns'The incidents come as rebel officials prepare for elections in the self-proclaimed Donetsk People's Republic and the Luhansk People's Republic on Sunday.
The elections were called after the leader of the Donetsk People's Republic, Alexander Zakharchenko, was killed in a bomb blast in the city of Donetsk in August. Rebel authorities have blamed Ukrainian operatives for the bombing.
The Ukrainian government has condemned the vote as illegal. On Saturday, President Petro Poroshenko accused Russia for being behind the "fake elections."
"They are conducted at gunpoint of Russian guns on occupied territory," Poroshenko said. "They are categorically unacceptable."
The Ukrainian leader also urged members of the G7, and Kyiv's partners from the European Union, the United States and Canada, to respond.
"We are absolutely convinced that nobody will recognize the election," Poroshenko said. "They do not correspond to Ukrainian judicial standards."
EU countries and the US have already declared the vote illegal and announced they would not recognize the outcome.
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dj/amp (AFP, Interfax, Ukrainski Novini)