The Kremlin warned on Saturday that the assassination of east Ukraine's main separatist leader was a provocation that would undermine the long-stalled Western-brokered peace deal and fuel tensions in the smouldering conflict.
Alexander Zakharchenko, the 42-year-old chief of the self-proclaimed Donetsk People's Republic, was killed in a bombing at a cafe in Donetsk in broad daylight Friday, becoming the four-year conflict's most prominent victim from the Moscow-backed side.
His bodyguard was also killed and 12 more people were injured. Moscow and rebel authorities have pointed the finger at Kiev, while Ukraine links the bombing to internal feuding and Russia's desire to control the territory.
Observers have expressed fears that the high-profile killing could fan the flames of a conflict that has been half-forgotten by the West amid crises elsewhere.
Officials led by President Vladimir Putin's spokesman said the former mine electrician's murder would further derail the Ukraine peace deal brokered by Germany and France in the Belarussian capital Minsk in 2015.
"This is no doubt a provocation," Kremlin spokesman Dmitry Peskov told Russian reporters.
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"Zakharchenko's death will certainly lead to increased tensions in the region" and undermine conditions for the "start of the implementation" of the so-called Minsk agreements.
Zakharchenko was a co-signee of the peace agreement, along with fellow rebel Igor Plotnitsky, the chief of the self-proclaimed Lugansk People's Republic, who was deposed in late 2017.
Germany and France have sought in recent months to revive the stalled peace process in a bid to end a conflict that has claimed the lives of more than 10,000 since April 2014.
Russia's top diplomat Sergei Lavrov also said Saturday that Zakharchenko's killing derailed the Minsk deal and ruled out any meetings with France, Germany and Ukraine to discuss the crisis in the so-called Normandy Format.
"This is a serious situation that has to be analysed," Lavrov was quoted as saying by Russian news agencies.
"What happened today puts a big question mark over the entire process," added Russian foreign ministry spokeswoman Maria Zakharova, speaking in televised remarks late Friday.
Putin on Friday swiftly sent condolences to Zakharchenko's family and residents of rebel-controlled Ukraine and seemed to imply that Kiev may be behind the murder.
"Those who have chosen the path of terror, violence and intimidation do not want to look for a peaceful, political settlement of the conflict, do not want to have genuine dialogue with residents of the southeast," Putin was quoted as saying by the Kremlin.
In east Ukraine, senior separatist commander Eduard Basurin claimed that Kiev planned to launch an offensive in mid-September, adding separatist troops had been put on high alert. Kiev has denied any such plans.
Rebel authorities declared a three-day period of mourning and delayed the start of a new school year until Tuesday.
The acting head of the region, Dmitry Trapeznikov, told reporters late Friday that local authorities had detained several suspects and they helped confirm that the blast was "an act of sabotage by Ukraine".
People in Donetsk openly wept at the news of Zakharchenko's death. "It is a tragedy for the entire Donbass," said Donetsk resident, Alexander Grigoryev, 61, referring to war-torn east Ukraine.
"It's such a pity. He could have been the leader of our country for a very long time," he said.
Zakharchenko -- who briefly worked as a mine electrician before going into business connected to the industry -- had led Russian-backed insurgents in the rebel region for the last four years.
He became the rebel prime minister in August 2014, taking over from a series of Russians who had held the post.
In November 2014, he was elected the first president of the Donetsk republic, facing no real opposition.
Zakharchenko, who liked to be seen wearing khaki military fatigues, sold his business to finance the rebels and took part in the storming of the Donetsk regional administration building that launched the conflict in 2014.