Over 60 people were killed and 145 were injured in Moscow on Friday after camouflage-clad gunmen opened fire inside a concert hall with automatic weapons, the Associated Press reported.

Terrorist organisation Islamic State claimed responsibility for the attack through a message by the group’s Amaq agency on Telegram. The shooting took place days after Russian President Vladimir Putin secured another six-year term in office in an election that was widely seen as a rigged exercise.

The gunmen on Friday went on a shooting spree just before Russian rock band Picnic was to perform at the 6,200-seat Crocus City Hall, Reuters reported. This was the deadliest attack in the country since 2004.

Videos on social media showed gunmen shooting at civilians inside the concert hall and people taking cover behind seats. Flames were later seen engulfing the building.

Authorities deployed helicopters to try and douse the fire. The roof of the venue was in danger of collapsing, state news agency RIA reportedly said.

Dave Primov, who was at the venue when the attack occurred, told AP: “There were volleys of gunfire. We all got up and tried to move toward the aisles. People began to panic, started to run and collided with each other. Some fell down and others trampled on them.”

It was unclear what happened to the attackers after the shooting. State authorities are investigating the attack as an act of terrorism.

Russian Foreign Ministry spokeswoman Maria Zakharova said it was a "bloody terrorist attack" that the whole world should denounce.

An unidentified United States official told AP that American intelligence agencies had gathered information that the Islamic State was planning an attack in Moscow, and had privately shared the details with Russian authorities.

India’s Prime Minister Narendra Modi said that the country strongly condemns the “heinous terrorist attack”. He said in a social media post: “Our thoughts and prayers are with the families of the victims. India stands in solidarity with the government and the people of the Russian Federation in this hour of grief.”