MOSCOW — The leader of the Donetsk People’s Republic, a Russian-backed separatist enclave in eastern Ukraine, was killed on Friday when a bomb exploded at a restaurant where he was having dinner, an attack that threatened to set off an escalation of the Ukraine war.

The spokeswoman for the Russian Foreign Ministry, Maria Zakharova, blamed the Ukrainian government, saying that “there is every reason to suggest that the Kiev regime stands behind this murder.” And Russia’s speaker of Parliament suggested that because the victim, Aleksandr Zakharchenko, was one of the parties who signed a peace agreement with Ukraine called Minsk II, that pact was no longer valid.

Ukrainians say Mr. Zakharchenko, a former electrician, filled a mostly figurehead position for the Russian security service agencies that manage and finance the breakaway regions of Donetsk and Luhansk, and they attributed his death to infighting in the rebel ranks or a Russian targeted killing.

Mr. Zakharchenko became the latest in a long list of separatist leaders to die in mysterious assassinations. He had reportedly dined often at the restaurant, which was paradoxically called Separ, short for separatist.