Authorities have reported that a group of armed men opened fire at a Crocus City concert hall and mall in Moscow, Russia, on Friday night, killing at least 115 people and injuring several others.

Russian authorities have tagged this one of the deadliest such attacks in Russia in recent decades. A video shared online showed at least two masked men entering the Crocus City Hall, with one repeatedly firing shots from what appeared to be an assault rifle.

Another graphic video showed four men, with at least three carrying weapons, chasing a group of people and firing at them point blank.

As reported by Conservative Archives, the terrorists were dressed in camouflage. They stormed the venue and opened fire at the audience inside the concert hall with what some reports indicate were automatic weapons. The terrorists also reportedly detonated a grenade, setting the Crocus City complex on fire.

Videos on social media shared by different Russian news outlets showed panicked concertgoers attempting to hide under seats and the sound of gunfire.

A Breitbart News report showed that Russian officials have arrested 11 people connected to the terror attack. Russia’s FSB security service revealed some of the terrorists had fled towards the Russia-Ukraine border, adding that the assailants had “appropriate contacts” in the Ukraine.

Some Russian lawmakers have, however, pointed accusatory fingers at Ukraine despite offering no evidence to back up their claim.

“The main interested party could most likely be Ukraine and its patrons … we can’t rule it out,” said senior Russian MP Andrey Kartapolov.

According to the Associated Press, Russian news reports identified the gunmen as citizens of Tajikistan, a former Soviet country in Central Asia that is predominantly Muslim and borders Afghanistan.

According to the outlet, many Russian hardliners called for a crackdown on Tajik migrants, but President Vladimir Putin rejected the idea, saying force would be able to sow the poisonous seeds of discord, panic or disunity in their multi-ethnic society.

He also declared Sunday a day of mourning and said that additional security measures have been imposed throughout Russia. This attack comes two weeks after the U.S. Embassy in Moscow issued a notice urging Americans to avoid crowded places because of imminent plans by extremists to target large Moscow gatherings, including concerts.

Several other Western embassies repeated the warning. However, earlier this week, Putin criticized the warning as an attempt to intimidate Russians.