Russia has charged four men it says attacked a Moscow concert hall and killed at least 137 people.

Three were marched blindfolded into a Moscow court while the fourth was in a wheelchair. All were charged with committing an act of terrorism.

The Islamic State group, or IS, said it carried out Friday's outrage at Crocus City Hall, and posted video.

Russian officials have claimed, without evidence, Ukrainian involvement. Kyiv says the claim is "absurd".

They were named as Dalerdzhon Mirzoyev, Saidakrami Murodali Rachabalizoda, Shamsidin Fariduni and Muhammadsobir Fayzov.

Video showed three of them being marched blindfolded by masked police into Basmanny district court in the Russian capital. All appeared injured.

Mirzoyev and Rachabalizoda's eyes were blackened and the latter's ear was heavily bandaged - reportedly from it being partially severed during his arrest.

Fariduni's face was badly swollen and Fayzov was brought into court in a wheelchair and appeared to have an eye missing, according to the Reuters news agency.

A court statement on the Telegram messaging service said Mirzoyev was a citizen of Tajikistan and "admitted his guilt in full". Rachabalizoda also "admitted guilt", it said.

All four are to be held in pre-trial detention until at least 22 May, the court added.

The men were arrested hours after four gunmen on Friday night stormed the Crocus City Hall, on the outskirts of Moscow, and began firing on some of the estimated 6,000 people who were attending a rock concert. The attackers also set fires which engulfed the venue and caused the roof to collapse.

Russian authorities said 137 people were killed and more than 100 injured.

IS claimed the attack within hours, stating that it was carried out by a branch known as the Islamic State in Khorasan, or IS-K, which is chiefly based in Afghanistan and Central Asia.

It later released graphic images of the attackers. US officials have said they have no reason to doubt that claim of responsibility.

However no Russian official has acknowledged the claim, instead suggesting - without evidence - that the attackers were being helped by Ukraine and were in the Bryansk region preparing to cross the border at the time of their arrest.

Ukraine's President Volodymyr Zelensky on Sunday rejected the claims, and his military intelligence directorate said it was "absurd" to suggest the men were trying to cross a heavily mined border, teeming with hundreds of thousands of Russian soldiers, to reach safety.