The Islamic State terrorist group claimed responsibility for a horrendous attack on civilians at the Crocus Concert Hall in Moscow, the capital of Russia.

Early reports said that four armed terrorists went on a murderous rampage at the concert hall as attendees fled in horror. Videos on social media captured some of the carnage, including civilians being shot at point-blank range.

The militants set off grenades and other explosives that caused the hall to catch on fire. Later, the roof of the building caved in, and firefighters worked for hours to put out the blaze.

Officials said that about 40 people had been counted dead and another 146 people have been injured in the heinous attack. It was unclear what happened to the attackers after the massive law enforcement response.

Hours later, the terror group claimed responsibility for the rampage in posts on social media, according to the Associated Press, and claimed that the militant fighters returned to their base safely.

"The images are just horrible and just hard to watch," said National Security Council spokesman John Kirby in a media briefing. "And our thoughts, obviously, are gonna be with the victims of this terrible terrible shooting attack."

Crocus is a popular shopping mall and concert venue in a suburb of Moscow.

Earlier in March, the U.S. embassy in Russia had issued a warning that an ISIS attack might be imminent after Russia was able to foil a terrorist plot against a Jewish synagogue in Moscow.

“The Embassy is monitoring reports that extremists have imminent plans to target large gatherings in Moscow, to include concerts, and US citizens should be advised to avoid large gatherings over the next 48 hours,” read a statement from the embassy.

On Friday, Kirby said that the previous warning was unrelated to the Crocus terror attack.

“I don’t think that was related to this specific attack," he said to reporters. “I’m not aware of any advance knowledge that we had of this terrible attack.”

The New York Times reported that U.S. officials confirmed that a branch of ISIS was responsible for the attack, namely Islamic State-Khorasan based in Afghanistan. The terror group has accused Russia of having blood on its hands as a result of previous military actions in Afghanistan, Syria, and Chechnya.

Here's more about the attack:

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