The attack on a Moscow concert hall on Friday was the worst in Russia for years. More than 100 people were killed as gunmen stormed the complex, days after President Vladimir Putin began his fifth term of office.
This is what is known about the attack.
Shooting begins
Crocus City Hall, on the outskirts of Moscow – about 20km (12 miles) from the Kremlin – was about to host a concert by the rock group Picnic when gunmen burst into the foyer at about 20:00 (17:00 GMT) on Friday evening.
Video showed at least four people in camouflage uniform shooting randomly before proceeding into the concert hall itself and opening fire there.
Inside the auditorium, a woman said she and other visitors rushed towards the stage as soon as they realised shots were being fired.
“I saw a person in the stalls with a sidearm and there were cracks [of gunfire] going off, I was trying to crawl behind a loudspeaker,” she told Russian TV.
At some point, fire can be seen inside the hall. Flames later engulfed the facade, while glass on the top two floors of the seven-storey building blew out.
“The terrorists used a flammable liquid to set fire to the concert hall’s premises, where spectators were located, including wounded,” Russia’s Investigative Committee said.
Helicopters were brought in to drop about 160 tonnes of water, but it took some 10 hours for the fire to be contained.
By the time the suspects escaped, hundreds had been killed and injured.
Many died from bullet wounds, some as a result of smoke inhalation.
Picnic’s band members themselves were unharmed.
Who are the victims?
More than 6,000 Russians had flocked to the retail and concert complex for the event.
The number of those who were killed has been rising steadily.
By midday on Saturday, at least 115 had been confirmed dead. The first official list of casualties suggested the oldest victim was in her 70s, with three children among the dead.
In addition to those killed, at least 60 remain in a serious condition and authorities have warned more could die.
Many of those killed and wounded came from Krasnogorsk, Khimki and other nearby towns on Moscow’s north-western fringe.
Who are the attackers?
It appears that those who carried out the attack managed to escape the inferno and mayhem they left behind and a manhunt began.
Russian MP Alexander Khinshtein said the attackers fled in a white Renault car. According to him, police tried to stop the vehicle in the Bryansk region, about 340km (210 miles) away from Moscow, managing to arrest two people as the others fled.
Some 14 hours after the first reports of shooting, Russia’s FSB security service announced 11 people had been arrested, including four “directly involved”.
Their identities have not been announced. Unconfirmed reports have mentioned nationals from Tajikistan – Mr Khinshtein said passports from the country had been found in the car.
Who was behind the attack?
A brief statement has been published by the Islamic State group (IS) in its media outlet Amaq, saying it was behind the attack.
Russian authorities have not commented on the claim, which comes two weeks after the US warned of a potential attack targeting “large gatherings” in Moscow. Russian officials have complained the US intelligence lacked specific detail.
The US had singled out ISIS-Khorasan or ISIS-K, an offshoot of IS which seeks to establish a Muslim caliphate across Afghanistan, Pakistan, Turkmenistan, Tajikistan, Uzbekistan and Iran.
Last week, President Vladimir Putin said: “Recent provocative statements by a number of official Westerns structures about the possibility of terrorist attacks in Russia… resembles outright blackmail and an intention to intimidate and destabilise our society.”
While the Russian authorities have not commented on the IS claim, Mr Putin said the assailants were caught as they were trying to flee to Ukraine.
The FSB said they had “relevant contacts” there, but no details have been given.
Ukraine has swiftly dismissed the Russian claims as “absolutely untenable and absurd”.
Russia launched a full-scale invasion of Ukraine in February 2022.