Pro-Russian rebels in eastern Ukraine have declared three days of mourning for a military commander who was killed on Sunday.

Arseny Pavlov, a Russian national known as “Motorola”, was blown up in the lift of his block of flats in Donetsk together with his bodyguard – according to rebel authorities.

Ukrainian sources in Kyiv have hinted at rebel in-fighting or an operation directed from Moscow.

But armed groups backed by the Kremlin have blamed Ukrainian special forces for his death.

“At the moment we are carrying out an investigation that will allow us to identify not only who ordered the murder – by the way we already know who he was – but also the contract killers,” said Aleksander Zakharchenko, head of the self-proclaimed People’s Republic of Donetsk, at a news conference.

Four armed masked men claimed responsibility for the killing in a video uploaded to the internet. They appeared alongside a flag belonging to a pro-Ukrainian neo-Nazi group. But reports say it has been labelled a fake.

Pavlov, who was 33, came to Ukraine in 2014 and took part in key battles against Ukrainian forces. In one interview he claimed to have murdered prisoners of war, prompting the government in Kyiv to launch a war crimes investigation.