Putin says 'radical Islamists' behind Moscow attack, links them to Ukraine

President Vladimir Putin on Monday acknowledged for the first time that "radical Islamists" were behind last week's attack on a concert hall outside Moscow, but suggested they were linked to Ukraine somehow.

Eleven people have been detained in connection with the attack, which saw camouflaged gunmen storm into Crocus City Hall, open fire on concert-goers and set the building ablaze, killing at least 139 people.

"We know that the crime was committed by the hands of radical Islamists, whose ideology the Islamic world itself has been fighting for centuries," Putin said in a televised meeting.

But the Russian leader said "many questions" remained unanswered, including why the attackers tried to flee to Ukraine -- a claim that Kyiv has rejected.

"Of course, it is necessary to answer the question, why, after committing the crime, the terrorists tried to go to Ukraine? Who was waiting for them there?" Putin asked.

"This atrocity may be just a link in a whole series of attempts by those who have been at war with our country since 2014," he said, referring to Ukraine and its allies.

Ukraine has described accusations it was involved as absurd.

"Putin was talking to himself again, and it was again broadcast on television. Again, he blames Ukraine," President Volodymyr Zelensky said in his evening address.

Islamic State jihadists have said several times since Friday that they were responsible, and IS-affiliated media channels have published graphic videos of the gunmen inside the venue.

The United States, which on March 7 warned about an "imminent" attack in Moscow by "extremists", has said IS bears "sole responsibility".

When asked about IS's claimed involvement, Kremlin spokesman Dmitry Peskov on Monday said that an investigation was still ongoing.

Officials expect the death toll to rise further, as rescuers were searching the site for remains on Monday and 97 people are still in hospital.

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