This story has been updated to reflect developments.
More than 130 people have been killed and 140 wounded at a Moscow show by Russian art-rockers Picnic. According to reports, four gunmen dressed in combat fatigues opened fire on the crowd at the 7300-capacity Crocus City Hall, before detonating explosives and setting the building on fire. The gunmen then fled the scene.
The attack comes two weeks after the UK and US embassies in Moscow issued warnings about extremist plans to target large gatherings in the city, including concerts, and less than a week after Russian presidential elections resulted in Vladimir Putin winning a fifth term in office.
Responsibility for the attack has been claimed by The Islamic State, who posted a statement on Telegram, the instant messaging service: "Islamic State fighters attacked a large gathering of Christians in the city of Krasnogorsk on the outskirts of the Russian capital, Moscow, killing and wounding hundreds and causing great destruction to the place before they withdrew to their bases safely."
Russian prosecutors have called the attack "an act of terrorism" and have opened a criminal case, while Russian Foreign Minister Maria Zakharova has called the attack a "monstrous crime" and urged the international community to condemn the action.
11 people have been detained in connection with the attack, including the four assailants, who, according to a speech by Vladimir Putin, were detained near the border with Ukraine. The four attackers were identified as being citizens of Tajikistan.
Earlier, former Russian president Dmitry Medvedev issued a statement on Telegram calling for action. "Terrorists understand only reciprocal terror," he wrote. "No trials or investigations will help if force is not answered with force, and deaths with total punishment of terrorists and repression of their families. That’s our worldly experience.
"If it can be established that these terrorists were from the Kyiv regime, it’s impossible to deal with them and those who have been inspired by their ideology any other way. They must all be found and ruthlessly destroyed as terrorists. Including official representatives of the state that committed such an atrocity."
The Ukraine Ministry of Foreign Affairs issued a statement in response, saying, "We consider such accusations to be a planned provocation by the Kremlin to further fuel anti-Ukrainian hysteria in Russian society, create conditions for increased mobilisation of Russian citizens to participate in the criminal aggression against our country and discredit Ukraine in the eyes of the international community."
"There's no indication at this time that Ukraine or Ukrainians were involved in the shooting," White House national security spokesperson John Kirby told reporters. "We're taking a look at it, but I would disabuse you at this early hour of any connection to Ukraine."
Earlier this month, Russia's Federal Security Service (FSB) said that it had prevented an attack on a synagogue in Moscow being plotted by Wilayat Khorasan, a cell of the Islamic State based in Afghanistan.
Moscow's mayor has cancelled all large-scale public events scheduled to take place over the weekend.
In November 2014, 90 fans were killed during a show by Eagles Of Death Metal at the Bataclan venue in Paris, during a series of coordinated terror attacks.
