MOSCOW — A bomb killed the most prominent pro-Russian rebel leader in the breakaway region of eastern Ukraine on Friday, Russian and Ukrainian officials said, heightening the tension in the region’s simmering proxy war.

Alexander Zakharchenko, the head of the self-declared Donetsk People’s Republic territory, died after a bomb blast at a cafe in Donetsk, local media reported.

Russia’s Foreign Ministry confirmed Zakharchenko’s death and blamed the government of Ukraine. Russian President Vladimir Putin warned that the incident could further destabilize a region that has been one of the major fault lines between the West and Russia.

Donetsk declared a state of emergency, canceled first-day-of-school celebrations and sealed off the city, according to Russian news reports. 

Pro-Russian rebels inaugurated Ukraine’s separatist leader Alexander Zakharchenko Nov. 4, 2014. Zakharchenko was assassinated Aug. 31, 2018, in Donetsk. (Reuters)

“There is every reason to believe that the Kiev regime is behind his murder,” Russian Foreign Ministry spokeswoman Maria Zakharova said, referring to the capital of Ukraine. “The Kiev war party is carrying out a terrorist scenario, worsening the already complicated situation in the region.”

On Ukrainian television, a senior Ukrainian intelligence official, Igor Guskov, confirmed Zakhar­chenko’s death and said that rival rebels or Russian spy services were behind the deadly blast.

The killing of Zakharchenko, who had led the Donetsk separatists since 2014, throws the four-year-old conflict in eastern Ukraine into a fresh phase of uncertainty.

A low-grade conflict between Russian-backed separatists and Ukraine has continued in recent months, with each side accusing the other of violating the peace agreements hammered out by Ukraine, Russia, Germany and France in Minsk, Belarus, in 2015. 

Departing from its policy in the nearby Ukrainian peninsula of Crimea, Russia never annexed the breakaway Donetsk and Luhansk territories in Ukraine’s Russia-friendly southeast.

Instead, after the pro-Western revolution in Kiev in early 2014, Russia provided military and financial support to rebels fighting the new Kiev government in a war that the United Nations said killed some 10,000 people and displaced hundreds of thousands. 

Putin issued a statement Friday praising Zakharchenko as a “courageous and decisive person, a patriot.” He stopped short of ­explicitly blaming Kiev for the killing but vowed that Russia would stand by the people of the region. 

“The despicable murder of Alexander Zakharchenko is the latest evidence that those who chose the path of terror, violence, and fear don’t want to seek a peaceful, political solution to the conflict, and don’t want to lead a real dialogue with the people of the southeast,” Putin said. “They are making a dangerous bet on destabilizing the situation.” 

The bomb on Friday struck a cafe in central Donetsk called Separ — as in “separatist.” Footage broadcast on Russian television showed the restaurant’s wrecked facade, with some columns still standing.

Alexander Timofeyev, a Donetsk government minister, was injured in the blast. 

Russian officials have blamed Ukraine for separatist assassinations in the past, with Kiev denying involvement. A bombing killed prominent rebel Arsen Pavlov, known as Motorola, in 2016, and a rocket killed separatist commander Mikhail Tolstykh, known as Givi, in his office in 2017. 

Guskov, the Ukrainian intelligence official, said on the 112 Ukraine television channel that Zakharchenko’s killing could have stemmed from a business dispute among the rebels or been organized by Russian spies.

“We don’t exclude that this was an effort by Russian intelligence agencies to eliminate a rather ­odious figure who, according to our information, was getting in the Russians’ way,” Guskov said. “According to our information, either the rebels or Russian intelligence agencies were behind this blast.”