Four men accused of involvement in the Moscow concert hall attack that killed at least 137 people were ordered in court to be detained pending trial.
All four have been accused of "terrorism" and risk a life sentence in prison, said a statement from Moscow's Basmanny district court.
They were ordered to be held until 22 May, but that could be extended depending on when the date for their trial is fixed.
The first two suspects were identified as Saidakrami Murodalii Rachabalizoda and Dalerdjon Barotovich Mirzoyev and face charges of a "terror attack committed by a group of individuals resulting in a person's death", according to Russian news agency TASS.
The court released a video showing police officers bringing one of the suspects into the courtroom in handcuffs, as well as photographs of the same man sitting in a glass cage for defendants.
Authorities said the suspects were foreign nationals.
According to Russian media and parliament member Alexander Khinstein, some of the suspects are from Tajikistan, a majority-Muslim former Soviet republic that borders Afghanistan.
Friday night's attack on Crocus City Call outside Moscow that killed 137 people and wounded over 180 was claimed by the Islamic State (IS).
Russian officials have so far not commented on that claim, suggesting instead that the suspects had links to Ukraine.
Kyiv denies any involvement in this attack, the deadliest in Russia since the early 2000s.
Earlier, Russia observed a national day of mourning after the deadliest attack in Europe to have been claimed by the Islamic State group.
Russian President Vladimir Putin has vowed to punish those behind the "barbaric terrorist attack", saying four gunmen trying to flee to Ukraine had been arrested.
Ukraine has strongly denied any connection, with Ukrainian President Volodymyr Zelensky accusing Mr Putin of trying to shift the blame onto them.
"The whole country is in mourning with those who lost their loved ones in this inhumane tragedy," public television channel Russia 24 said this morning.
Mr Putin, in his first public remarks on the attack, made no reference to a statement by IS claiming responsibility.
The Islamic State group yesterday wrote on Telegram that the attack was "carried out by four IS fighters armed with machine guns, a pistol, knives and firebombs," as part of "the raging war" with "countries fighting Islam".
A video lasting about a minute and a half, apparently shot by the gunmen, has been posted on social media accounts typically used by IS, according to the SITE intelligence group.
The video appears to have been shot from the lobby of the concert venue and shows several individuals with blurred faces and garbled voices, firing assault rifles with inert bodies strewn about and a fire starting in the background.
The attack was the deadliest in Russia for almost two decades.
Russian officials expect the death toll to rise further, with more than 150 wounded.
Russia's investigative committee, which probes major crimes, said rescue workers were still pulling bodies from the burnt-out building yesterday.
The emergency situations ministry has so far named 29 of the victims, the blaze having complicated the process of identification.
The ministry has posted a video of heavy equipment arriving at the scene of the fire to dismantle damaged structures and clear debris.
'Barbaric'
"Terrorists, murderers, non-humans ... have only one unenviable fate: retribution and oblivion," Mr Putin said in his televised address yesterday.
Calling the attack a "barbaric, terrorist act", he said "all four direct perpetrators ... all those who shot and killed people, have been found and detained".
Russian television showed security services interrogating four bloodied men, who spoke Russian with an accent, on a road in the western Bryansk region, which borders both Ukraine and Belarus.
"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," said Mr Putin.
Mr Zelensky, in his evening address yesterday, dismissed the suggestion that Kyiv had been involved.
"What happened yesterday in Moscow is obvious," he said. "Putin and the other scum are just trying to blame it on someone else."
Russia has arrested 11 people in connection with the attack, the FSB security service said. Earlier, the agency had said the attackers had "contacts" in Ukraine, without elaborating.
Site search to continue
Mr Putin, whose first public remarks came more than 18 hours after the start of the attack, declared today a day of national mourning.
"All the perpetrators, organisers and those who ordered this crime will be justly and inevitably punished," he promised.
The Investigative Committee said the death toll had so far reached 137 and the governor of the Moscow region said rescuers would continue to scour the site for "several days."
About 107 people were still in hospital, many in a critical condition, Deputy Prime Minister Tatyana Golikova said.
IS had first claimed responsibility for the attack on Friday night, repeating its claim again yesterday.
Some witnesses filmed the gunmen from the upper floors as they walked through the stalls shooting people, sharing the footage on social media.
Then "the terrorists used a flammable liquid to set fire to the concert hall's premises, where spectators were located, including wounded," the investigative committee said.
Investigators said people died from gunshot wounds as well as smoke inhalation after a fire engulfed the 6,000-seater venue.
Investigators said a man who jumped on one of the gunmen as he was shooting at the concert-goers, "immobilising" him and thus "saving the lives of people around him", would receive an award.
Blood donation queues
In Washington, a statement from the White House condemning the attack described the IS as a "common terrorist enemy that must be defeated everywhere".
The Russian interior ministry said all four of the suspected gunmen were foreign nationals.
Russian Telegram channels - including those with links to the security services - said they were from Tajikistan, a country that borders Afghanistan and where the jihadist group is active.
Tajikistan's foreign ministry told Russia's TASS news agency it was in close contact with Moscow over the matter.
In Moscow, residents stood in long queues in the rain to donate blood for those in hospital, and mourners came to lay flowers outside the concert hall.
Memorial posters featuring a single candle replaced some advertising billboards in the capital and major events were cancelled across the country.
Museums, theatres and cinemas announced their closure over the weekend.
US warning dismissed
Just three days earlier, Mr Putin had publicly dismissed a US warning of an "imminent" attack in Moscow as propaganda designed to scare Russian citizens.
The US embassy in Russia had warned on 7 March that "extremists have imminent plans to target large gatherings in Moscow, to include concerts", advising caution over the following 48 hours.
Washington said after the attack it had also shared details directly with Moscow.
But speaking to FSB chiefs last Tuesday, Mr Putin had called it a "provocative" statement and "outright blackmail ... to intimidate and destabilise our society".
Explainer: What we know about the the Moscow concert hall attack
ISIS-K: The group behind Moscow attack and their motives
Watch: Eyewitness takes cover as gunfire heard in Russian venue
