A roadside bomb killed five US troops in southern Afghanistan on Saturday, officials said, in the biggest attack on NATO-led forces since the Taliban launched their \"spring offensive\" a week ago. \"Five American soldiers were killed at about noon when their armoured vehicle hit a powerful roadside mine in Maiwand district,\" Kandahar province\'s police chief General Abdul Razeq told AFP. The troops died in an improvised explosive device (IED) attack, NATO\'s International Security Assistance Force confirmed in a statement without specifying the nationalities of the victims, in line with coalition policy. The attack came four days after three British soldiers were killed in a similar attack in the neighbouring province of Helmand. There was no immediate claim of responsibility but Taliban militants frequently use roadside bombs against US-led foreign troops and their Afghan allies. Afghan police and soldiers are taking over responsibility for security, but there is growing concern over the war-torn country\'s prospects after 2014 when all foreign combat deployments will finish.