AMERICAN and British troops poised to assault the Taliban stronghold of Marjah have begun targeting insurgent leaders for assassination.

Military sources said special forces had been infiltrating the town on “kinetic” missions — jargon for armed attacks. “Special forces guys have been going in on assassination missions with the aim of decapitating the Taliban force,” one said.

At the British base of Camp Bastion and the adjoining Camp Leatherneck, the US marine base, troops and munitions have been airlifted in by night to avoid enemy rockets. It is clear that international forces are on the brink of a big battle. All yesterday morning, the thud-thud-thud of heavy machineguns and the crump of mortars filled the air.

In a break from traditional military secrecy, American, British and Afghan commanders have announced that Marjah, the last town in Helmand under Taliban control, will be attacked.

Operation Moshtarak (“Together”) will be by far the largest offensive since General Stanley McChrystal, the American commander of Nato forces in Afghanistan, instigated his counter-insurgency strategy, backed by President Barack Obama’s 30,000-troop “surge”.

About 1,000 Taliban, mostly Afghans but with some foreign fighters in their ranks, are believed to be in Marjah, an opium centre and local headquarters for bomb-making and sending out suicide bombers.

The risks are huge. By surrendering the element of surprise, the coalition has given the insurgents time to dig in and expand an already extensive tunnel network. Taliban diehards are known to have been placing bombs along alleyways, roads and in a network of irrigation canals.