There was a heavy police presence around the Basmanny District Court, which is expected to determine pre-trial restrictions for the men suspected of opening fire on crowds of concertgoers at the suburban Crocus City Hall on Friday.

One of the suspects was led blindfolded into the courtroom. His blindfold was removed and a black eye was visible.

The attack, which has been claimed by an affiliate of the so-called Islamic State, was the deadliest on Russian soil in years.

Authorities arrested four suspected attackers on Saturday, with seven more detained on suspicion of involvement in the attack, Russian President Vladimir Putin said in a night-time address to the nation, on Saturday.

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

Family and friends of those still missing waited for news of their loved ones as Russia observed a day of national mourning on Sunday.

Events at cultural institutions were cancelled, flags were lowered and TV entertainment and ads were suspended, according to state news agency RIA Novosti.

A steady stream of people took flowers to a makeshift memorial near the Crocus City Hall music venue.

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

As rescuers continue to search the damaged building, some families still do not know if members who went to the event targeted by gunmen on Friday are alive.

Igor Pogadaev was desperately seeking any details of his wife’s whereabouts after she went to the concert and stopped responding to his messages.

He has not seen a message from Yana Pogadaeva since she sent her husband two photos from the venue.

After Pogadaev saw the reports of gunmen opening fire on concertgoers, he rushed to the site but could not find her in the numerous ambulances or among the hundreds of people who had made their way out of the venue.

“I went around, searched, I asked everyone, I showed photographs. No one saw anything, no-one could say anything,” he said.

As the death toll mounted on Saturday, Pogadaev scoured hospitals in Moscow and the Moscow region, looking for information on newly-admitted patients.

His wife was not among the 154 reported injured, nor on the list of 50 of the 133 fatalities who authorities have already identified, he said.

The Moscow region’s emergency situations ministry posted a video on Sunday showing equipment dismantling the damaged music venue to give rescuers access.

Putin 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.

Kyiv strongly denied any involvement and the IS group’s Afghanistan affiliate claimed responsibility.

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 fervor for Russia’s fight in Ukraine, which recently entered its third year.

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

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

– AAP