Russian media reported on Friday that 18 people were killed and 43 others injured in a shooting incident at the "Crocus City Hall" concert hall near Moscow.

A video showed flames rising into the sky and columns of black smoke rising above the site.

Moscow Mayor Sergey Sobyanin said: "A terrible tragedy occurred at the Crocus City shopping center today."

"I am sorry for the victims' loved ones."

Sobyanin confirmed that all necessary assistance would be provided to those injured in the incident.

Russian official news agencies said police and other emergency services arrived at the scene. Some people were still inside the concert hall.

In an unverified video posted on social media, men carrying automatic weapons appeared repeatedly shooting at screaming civilians, including women, who were hiding under what appeared to be an entrance sign to "Crocus City Hall."

Other video footage showed a number of people lying motionless in pools of blood outside the hall. Reuters could not immediately verify the footage.

Another video showed the attackers shooting at people inside the concert hall.

Earlier this month, the U.S. Embassy in Russia warned that "extremists" had imminent plans to launch an attack in Moscow.

It issued its warning hours after the Russian Federal Security Service (FSB), the main successor to the Soviet-era KGB, announced it had thwarted an attack on a Jewish temple in Moscow carried out by an Islamic State cell.