Nato-led forces say they are making good progress after launching the biggest offensive in Afghanistan since the overthrow of the Taliban in 2001. There were clashes as more than 15,000 US, Britain and Afghan troops swept into the Helmand areas of Marjah and Nad Ali in a bid to secure government control. According to Afghan officials five militants have been killed so far since the offensive began on late Friday night The Afghan Army said 70 per cent of Marjah had been cleared, while a British commander said 11 Taliban bases had been captured. The US marines led the attack on Marjah while to the north, British, Canadian and other American forces moved on Nad Ali. According to NATO, Marjah is home to the biggest community under insurgent control in the south, with between 400 and 1,000 militants based there before the operation was launched. Operation Moshtarak, which means "together" in the local Dari language, is being led by the US Marine Corps, supported by 4,000 British troops, with Canadians, Danes and Estonians Afghan President Hamid Karzai warned troops to avoid civilian casualties. The operation is part of an effort to secure a 320-kilometre horseshoe-shaped string of towns that runs along the Helmand River, through Kandahar and on to the Pakistani border. Meanwhile, Afghan President Hamid Karzai warned troops to avoid civilian casualties.Three US soldiers with the NATO-led International Security Assistance Force (ISAF) have been killed in a roadside bomb in south of Afghanistan . According to a local official Captain Abdul Rahman, a suicide bomber riding a motorbike targeted the joint patrol of Afghan and NATO soldiers in Kandahar this morning inflicting casualties on U.S. troops and civilians.