A British Marine was killed in action in southern Afghanistan on Tuesday, the Ministry of Defense said. The marine, who was not identified, was serving with 42 Commando, Royal Marines in the Kajaki area of Helmand province when his unit came under fire, the ministry said. It said the marine had not been taking part in a major NATO offensive currently under way against Taliban militants in Helmand. Helmand province, where Britain has more than 5,000 troops, has seen a number of clashes with resurgent Taliban forces in the last few weeks. The latest death brings to 51 the number of British troops killed since a US-led invasion overthrew Afghanistan's Taliban regime in November 2001.