Ukraine had 'no involvement' in Moscow attack: White House

Putin has vowed to punish those behind the "barbaric terrorist attack" - but in his only public remarks on the massacre he made no reference to IS's claims of responsibility.

Instead he said four gunmen trying to flee to Ukraine had been arrested.

"They tried to escape and were travelling towards Ukraine, where, according to preliminary data, a window was prepared for them on the Ukrainian side to cross the state border," he said in a televised address to the nation on Saturday.

Kyiv has strongly denied any connection, with Ukrainian President Volodymyr Zelenskyy accusing Putin of trying to shift the blame onto them.

IS-K is a Sunni militant group that emerged from Afghanistan's eastern Nangarhar province around 2015, and hopes to install a hardcore Islamic caliphate spanning India, Iran and Central Asia.

The group has carried out dozens of attacks in Afghanistan and Pakistan. Under the Taliban, which regards it as an enemy, analysts say its efficacy inside Afghanistan has been eroded -- but that in recent months it has stepped up its activities globally.