The actions of Ukraine’s government in Kiev instigated this week's renewed clashes between Ukrainian government forces and pro-Russia separatist rebels in eastern Ukraine, a Kremlin spokesman said Friday. An indeterminate number of combatants on either side of the conflict were killed Wednesday in Donetsk in what was described as one of the biggest violations of the cease-fire agreement signed last February in Minsk.

The Organization for Security and Cooperation in Europe, a watchdog group which monitors the eastern Ukraine conflict, said “rebel initiative” likely caused fighting to break out this week near Marinka in Ukraine’s Donetsk province, the Associated Press reported. Separatist rebel leaders have reportedly disputed that account and claimed they acted in self-defense after a Ukrainian offensive. Meanwhile, Kremlin spokesman Dmitry Peskov said the battle was “about the provocative actions of Kiev” but did not provide any evidence.

“The most important thing for us is to facilitate in every possible way the implementation of the Minsk agreements. The Russian side uses every bit of leverage to influence the conflicting parties,” Peskov told reporters, as quoted by Russian-owned outlet TASS. “We still profoundly regret and are deeply concerned about Kiev’s failure to observe provisions of the Minsk agreements.”

It is unclear how many government and rebel soldiers were killed in this week’s fighting. Ukrainian representatives said five of their soldiers and approximately 80 rebels were killed. Rebel representatives officially said 14 separatists were killed, though others purportedly admitted to the AP that they had “likely lost dozens of men.”

The OSCE’s report also documented the use of heavy weapons and artillery in eastern Ukraine. The cease-fire’s terms called for both the Ukrainian government and rebel forces to withdraw such weapons from the conflict’s front lines. Prior to this week, the peace agreement has largely held in place, with occasional outbreaks of artillery fire and gun battles.

More than 6,400 people have died in the eastern Ukraine conflict since it began in early 2014. Western nations in the European Union and the NATO military alliance have repeatedly accused Russia of maintaining a presence in the area and of providing direct support to separatist rebels. The Kremlin has denied these accusations.