A major anti-terror operation is underway in Russia's North Caucasus. Thirteen militants and two policemen have been killed and a major terrorist attack involving massive quantities of explosives prevented.

­Two servicemen and six militants were killed in the Republic of Dagestan when a group of militants attacked a column of Russian soldiers. The incident happened while a search operation was underway in a forested area where troops were looking for the militants who had fired on government forces on Tuesday night. Reports say the shootout is continuing (as of 14.00 GMT).

Meanwhile the Chechen leader, Ramzan Kadyrov, has said seven further insurgents, including a militant leader, were killed in Chechnya today.

Russian security forces have also defused a large bomb not far from the area where the fighting is taking place in Dagestan. It was reported to be equivalent in strength to 100 kilograms of TNT and was also loaded with shrapnel components. The remote-controlled device was hidden in a pipe and left inside a car, which was parked near local market.

Officials say they have to thank local people who first noticed the suspicious vehicle and called the police.

On Monday, another terrorist attack was prevented in the Moscow Region, when the Russian security service FSB detained members of a subversive group who were planning a bomb attack on the high-speed Moscow-St Petersburg express train.