Russia is observing a day of mourning after at least 137 people were killed in an attack on Friday evening at a packed concert venue in Moscow.
Flags are flying at half mast, many events have been cancelled and TV channels have updated their schedules.
More than 140 people were also injured when gunmen entered the Crocus City Hall, firing indiscriminately before setting it on fire.
The Islamic State (IS) group says it was behind the attack.
Russia said on Saturday it had arrested all four gunmen suspected of carrying out a shooting massacre in a concert hall near Moscow, and President Vladimir Putin pledged to track down and punish those behind the attack.
Militant group Da’ish claimed responsibility for Friday’s rampage but there were indications that Russia was pursuing a Ukrainian link, despite emphatic denials from Ukrainian officials that Kyiv had anything to do with it.
In a televised address, Putin said 11 people had been detained, including the four gunmen. “They tried to hide and moved towards Ukraine, where, according to preliminary data, a window was prepared for them on the Ukrainian side to cross the state border,” he said.
