A firefighter attends to a fire at a market in Donetsk after shelling between Ukrainian forces and pro-Russian separatists June 3, 2015. (Aleksey Filippov/AFP/Getty Images)

Continued skirmishes between pro-Russian rebels and government forces in eastern Ukraine escalated Wednesday into the first major battle in months, leaving at least 18 dead and further threatening a tenuous cease-fire agreement signed in February.

Both sides traded accusations about who had started the fighting in Marinka, a suburb of ­Donetsk on the government-held side of the cease-fire line. Separatists reported 15 dead, and three Ukrainian soldiers were killed, according to a Facebook post
by Yuriy Biryukov, an adviser
to Ukrainian President Petro ­Poroshenko.

“They tried to move forward. The Ukrainian military are repelling all attacks, and the situation is under control,” Col. Andriy ­Lysenko, a spokesman for Ukraine’s National Security and Defense Council, said at a news conference Wednesday in Kiev. “Marinka and Krasnohorivka are under our control.”

But the head of the separatists’ militia said they were only defending themselves against an assault by the pro-Kiev forces.

“Trying to announce that we are storming Marinka — this is a provocation by Kiev,” said Vladimir Kononov, the militias’ top defense official. “We already are in Marinka.”

The fighting and resulting deaths were reminiscent of confrontations that have continued since February without erupting into major battles.

Since February, top diplomats from the United States and Europe have participated in several rounds of shuttle diplomacy aimed at settling the conflict and persuading the rebels and the government to fully implement the peace agreement signed in Minsk, Belarus.

Last month, U.S. Secretary of State John F. Kerry and Assistant Secretary of State Victoria Nuland made back-to-back trips to Russia, urging that country’s leaders to use their influence over the separatists in eastern Ukraine to push them to parley with Kiev. Groups from both sides were supposed to conclude an opening round of talks in Ukraine this week to address various points of contention.

Ukrainian Prime Minister Arseniy Yatsenyuk accused Russia on Wednesday of intentionally undermining the peace process and ordering pro-Russian separatists in Ukraine “to start a military operation.”

Ukraine and its Western allies have long accused Russia of fueling and effectively controlling the separatist uprising in eastern Ukraine with troops, weapons and other military supplies.

The surge in violence also comes as Western nations are gearing up for this weekend’s Group of Seven summit in Germany — an assembly of nations from which Russia was ousted when it annexed Crimea last year.

That annexation happened after the upper house of the Russian parliament met in an emergency session to give President Vladi­mir Putin the authority to send troops abroad.

A Praviy Sektor (Right Sector) fighter, aged 70, poses for a pictures at their headquarter in a village near Pokrovskoe. Right Sector is a paramilitary group that fights with the governmental army against separatists for the control of the East of Ukraine. (Fabio Bucciarelli/AFP/Getty Images)

On Wednesday, the speaker of the upper house told lawmakers that there may be cause to hold a similar emergency session soon but did not give a specific reason for the warning.

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