Moscow: Amid Russia's intense military campaign against ISIS in Syria, as many as 10 militants from a gang that swore allegiance to the Islamic State have been killed after a firefight between Russian special forces and the terrorists near the city of Nalchik in Russia's North Caucasus.

According to National Counter-Terrorist Committee, the counter-terrorist operation is currently underway in a mountainous region near Nalchik, Russia Today reported.

The operation began early Sunday morning in woodland adjacent to Nalchik, the capital of Kabardino-Balkaria Republic. A unit searching a territory near the city spotted a group of militants in a dug-out on Saturday.

The Russian military, over the last month, has conducted bombing missions in Syria and fired multiple cruise missiles at the IS stronghold of Raqqa, a Syrian city.

Russia has vowed to escalate its military campaign against IS in Syria after it confirmed the Metrojet airliner that crashed in the Sinai, killing 224 passengers, was brought down by a bomb.

Meanwhile, having vowed to escalate its military campaign against the ISIS, the Russian airmen have inscribed 'That's for Paris' on the side of one of the bombs they plan to use against the terrorist organisation in Syria, a media report said.

A picture of the bomb was shared from the official Twitter account of the Russian Embassy in Britain, the Independent reported.

British Defence Secretary Michael Fallon previously criticised the strikes, saying they may have killed "several hundred" civilians.

Several coordinated gun and suicide bombing attacks on the French capital by Islamists killed 129 people on November 13.

(With inputs from agencies)