Moscow: Several gunmen fired shots at a concert hall in Moscow on Friday, the Associated Press reported, citing Russia’s state RIA Novosti news agency. Russia's Federal Security Service has stated that 40 people have died and more than 100 have been injured. No group, thus far, has claimed responsibility for the attack.

According to the RIA Novosti report, at least three people in combat fatigues had opened fire on the visitors at the concert hall with automatic weapons. The state Tass news agency also reported the shooting at the Crocus City Hall, a huge concert hall on the western edge of the Russian capital where a crowd had gathered for a performance of the band Picnic.

Some purported videos of the attack have shown a fourth attacker being involved in the incident. 

Several other Russian media outlets reported the shooting and said that the hall was on fire. Video posted on Russian messaging app channels showed huge plumes of black smoke rising over the building. Quoting local news reports, the Associated Press said that the fire may have been caused by the assailants throwing explosives during the attack. 

Russian authorities have tightened security at Moscow's airports and railway stations. The mayor of Moscow has also announced the cancellation of all mass gatherings scheduled for this weekend.

Reacting to the incident, White House National Security Advisor John Kirby said that while he could not speak about the details of the attack, “the images are just horrible. And hard to watch.”

“Our thoughts are going to be with the victims of this terrible, terrible shooting attack. There are some moms and dads and brothers and sisters and sons and daughters who haven’t gotten the news yet. This is going to be a tough day," he added. 

US Embassy in Moscow had Warned of Imminent Attack

The attack followed a statement issued earlier this month by the US Embassy in Moscow that urged the Americans to avoid crowded places in the Russian capital in view of an imminent attack, a warning that was repeated by several other Western embassies, the Associated Press reported. 

When asked about the embassy's notice issued on March 7, John Kirby referred the question to the State Department, adding: "I don’t think that was related to this specific attack.”

Russia's Investigative Committee Investigating Concert Hall Incident as Terrorist Attack

The Associated Press has reported that Russia's top investigative agency has now opened a criminal probe into the incident and is investigating it as a terrorist attack. 

International Community Obliged to Condemn this Attack: Moscow

Following the attack, the Russian foreign ministry issued a statement on its social media accounts stating that ‘ordinary citizens’ from around the world are calling to offer their condolences following the city hall attack. 

Foreign ministry spokesperson Maria Zakharova said that the international community is “obliged to condemn this bloody terrorist attack in Moscow”.