American commanders gave notice on Wednesday that the assault is imminent.
British and Afghan forces will flood into a Taliban enclave in southern
Helmand province in a massive show of force intended as a decisive
start to President Barack Obama's "surge" of 30,000 extra troops.
The operation is expected to involve up to 15,000 personnel and could last between six and eight weeks.
They are preparing to take the town of Marjah which they describe as a "festering sore" after last summer's Helmand offensives.
town has been described as a nexus of militant fighters, bomb makers
and opium traffickers and is believed to have given sanctuary to many
fighters who fled British and US operations in central Helmand last
US officers believe between 600 and 1,000 fighters, including 150 foreign volunteers, are in the district.
forces have met sporadic gunfights and roadside bombs as they have
manoeuvred on the town in recent weeks, but predict many will flee a
determined offensive leaving a hard core.
Col George Amland,
deputy commander of UN marines in Helmand, predicted Taliban ranks
would "dwindle very quickly into a very manageable number" as the
Taking Marjah would fill in gaps and refuges left
after last summer's Operation Sword Strike along the southern Helmand
He said: "We are going to gain control of a capital
investment they have had control of for some time. We are going to
alter the ecosystem here considerably." Marjah district is surrounded
by irrigation canals built in the 1950s and 1960s with American aid.
The district is home to around 125,000 people, including 80,000 in the