Four men accused of staging the Russia concert hall attack that killed more than 130 people have appeared before a court showing signs of severe beatings as they faced formal terrorism charges.

One appeared to be barely conscious during the hearing on Sunday.

A court statement said two of the suspects accepted their guilt in the assault after being charged in the preliminary hearing, though the men’s condition raised questions about whether they were speaking freely.

There had been earlier conflicting reports in Russian media outlets that said three or all four men admitted culpability.

Moscow’s Basmanny District Court formally charged Dalerdzhon Mirzoyev, 32; Saidakrami Rachabalizoda, 30; Shamsidin Fariduni, 25; and Mukhammadsobir Faizov, 19, with committing a group terrorist attack resulting in the death of others.

The offence carries a maximum sentence of life imprisonment.

The court ordered that the men, all of whom are citizens of Tajikistan, be held in pre-trial custody until May 22.

Russian media had reported that the men were tortured during interrogation by the security services, and Mirzoyev, Rachabalizoda and Fariduni showed signs of heavy bruising, including swollen faces, with Rachabalizoda also having a heavily bandaged ear.

The fourth suspect, Faizov, was brought to court from a hospital in a wheelchair and sat with his eyes closed throughout the proceedings.

Court officials said Mirzoyev and Rachabalizoda admitted guilt for the attack after being charged.

The hearing came as Russia observed a national day of mourning for the attack on Friday on the suburban Crocus City Hall concert venue that killed at least 137 people and left 182 people injured.

The attack, which has been claimed by an affiliate of the Islamic State group, is the deadliest on Russian soil in years.

Mukhammadsobir Faizov, a suspect in Friday’s shooting at the Crocus City Hall, sits in a glass cage in court on Sunday. Photo: AAP

Russian authorities arrested the four suspected attackers on Saturday, with seven more people detained on suspicion of involvement in the attack, Russian President Vladimir Putin said in an address to the nation on Saturday.

He claimed they were captured while fleeing to Ukraine, something that Kyiv firmly denied.

Cultural events were cancelled on Sunday, flags were lowered to half staff and television entertainment and advertising were suspended.

A steady stream of people added to a makeshift memorial near the burned-out concert hall, creating a huge mound of flowers.

Rescuers continued to search the damaged building and the death toll rose as more bodies were found as family and friends of some of those still missing waiting for news.

Moscow authorities began identifying the bodies of those killed via DNA testing, saying the process would take at least two weeks.

Putin has called the attack “a bloody, barbaric terrorist act” and said Russian authorities captured the four suspects as they were trying to escape to Ukraine through a “window” prepared for them on the Ukrainian side of the border.

Russian media broadcast videos that apparently showed the detention and interrogation of the suspects, including one who told the cameras he was approached by an unidentified assistant to an Islamic preacher via a messaging app and paid to take part in the raid.

Putin did not mention IS in his speech to the nation, and Kyiv accused him and other Russian politicians of falsely linking Ukraine to the assault to stoke fervour for Russia’s fight in Ukraine, which recently entered its third year.

US intelligence officials said they had confirmed the IS affiliate’s claim.

“ISIS bears sole responsibility for this attack. There was no Ukrainian involvement whatsoever,” National Security Council spokeswoman Adrienne Watson said.

The US shared information with Russia in early March about a planned terrorist attack in Moscow, and issued a public warning to Americans in Russia, Watson said.

The raid was a major embarrassment for Putin and happened just days after he cemented his grip on the country for another six years in a vote that followed the harshest crackdown on dissent since the Soviet times.

IS, which fought against Russia during its intervention in the Syrian civil war, has long targeted Russia.

In a statement by the group’s Aamaq news agency, the IS Afghanistan affiliate said it had attacked a large gathering of “Christians” in Krasnogorsk.