Pro-Russian rebels in eastern Ukraine are trying to find out who assassinated one of their commanders, considered a war criminal by Ukrainian authorities.
Russian-born Arsen Pavlov, nicknamed “Motorola”, was killed by a bomb blast in the lift of his apartment block in the city of Donetsk on Sunday.
The rebels accused Ukraine’s President Petro Poroshenko of declaring war.
A video appeared online purportedly from a Ukrainian neo-Nazi group claiming it had killed Motorola.
But the claim from the mysterious “Misanthropic Division” has to be treated with great caution, the BBC’s Tom Burridge in Kiev says. Propaganda, often vicious and cynical, is a feature of the conflict, he says.
Little is known about the “division”. The clip was tweeted by Alexander Kots, a Russian war correspondent, and showed four masked men with guns.
The division’s leader says his group had nothing to do with the video.
Motorola commanded a rebel battalion called Sparta, which took part in major offensives against Ukrainian government forces at Donetsk airport and Ilovaisk.
Ukraine accused him of war crimes.
Born in Komi, northern Russia, in 1983, Motorola called himself a “volunteer”, the term used by the Kremlin for all Russians fighting in rebel ranks. Many of the rebel commanders are Russian citizens.
Last month President Poroshenko said Motorola had shot and killed a Ukrainian prisoner-of-war, Ihor Branovytsky, and said “the monster will answer” for that crime, the daily Ukrainskaya Pravda reported (in Russian).
In April last year Motorola told the Kiev Post that he had shot dead 15 Ukrainian soldiers captured by the rebels.
Commenting on the assassination, Donetsk rebel leader Alexander Zakharchenko said: “As I understand it, Petro Poroshenko has violated the ceasefire and declared war on us.”
He described the killing as “terrorism”.
Russia backs the rebels, who run a self-declared “Donetsk People’s Republic” (DNR).
Rebel commander was Russian veteran – by Tom Burridge in Kiev:
The video posted online must be treated with great care.
It is striking that the men make a Nazi salute. But little is known about the group mentioned and there are already reports that the video is a fake.
There are some far-right groups in Ukraine and far-right battalions in the army enjoyed some success early on in the war.
However, Russian propaganda has overblown their importance and, in an almost farcical way, has portrayed the conflict in the east as a struggle against fascism.
In reality, far-right political parties enjoy minimal support in Ukraine.
Pavlov was born in Russia, previously served in the Russian military in Chechnya, and rose to prominence in the DNR militia during key battles in eastern Ukraine.
Many Ukrainians have reason to want him dead.
In a chilling taped phone call last year, Pavlov admitted killing Ukrainian prisoners-of-war.
Eastern Ukraine’s unrecognised separatist republics are international pariahs and therefore economically dependent on Russia.
And Russian money, Russian culture and propaganda shape the discourse in these two isolated, war-torn regions.
According to some reports, an ethnic Abkhaz commander in the rebel ranks had fallen out with Motorola and may have been motivated to have him killed.
The continuing use of heavy weapons along the front line in eastern Ukraine is undermining the fragile ceasefire.
Ukraine, Western leaders and Nato say there is clear evidence that Russia has supplied the rebels with heavy weapons and regular troops. Russia denies that, but it is hostile to the Kiev government and openly supports the rebel cause.
In the video, the “Misanthropic Division” warned that it would next target Mr Zakharchenko and Igor Plotnitsky, the rebel leader in the neighbouring Luhansk region.
‘Motorola’: Ukraine rebels accuse Kiev over commander’s death