KANDAHAR: Thousands of people are leaving their homes on the Marjah plain in southern Afghanistan ahead of a massive military operation to clear Taliban militants from their last stronghold.

A huge force of US Marines leading NATO and Afghan soldiers is expected to launch the operation -- which commanders say will be the largest assault against the militants since the war began -- within days.

"The government of Afghanistan will reclaim Marjah as one of its own," said the British commander of the operation, General Nick Carter.

The assault is known as Operation Mushtarak -- Dari for "together", as Afghan troops will also play a pivotal role -- and has been flagged by military officials for months to either repel or draw in the enemy.

Taliban leaders say they are massing fighters around Marjah, in the centre of Helmand province, in preparation for a bloody battle.

"We are in control and ready to fight," said purported Taliban spokesman Yousuf Ahmadi, speaking by telephone from an undisclosed location.

The area is said to be the last bastion of control for the militants, whose insurgency has nevertheless been spreading since their regime was overthrown in 2001.

Mushtarak echoes assaults last year -- the British Operation Panther's Claw and the Marines' Operation Dagger -- seen as successfully eradicating militants who had controlled other poppy-growing regions in Helmand valley.

Preparatory operations around Marjah, south of the provincial capital Lashkar Gah, have been going on for weeks, with leaflets dropped on the area from NATO helicopters warning residents of the assault to come.

Habibullah, 48, said he and his family left Marjah for Lashkar Gah two months ago to escape the violence.

"There are a lot of Taliban there. They are violent towards us, accusing us of spying for the foreign forces, demanding food all the time," he told AFP.

"There are still people living there and the Taliban are still in control, but there has been a lot of fighting, with gunfire and bombings, and lots of soldiers have been coming in to fight the Taliban and then leave," he said.

The battle to come is expected to be hard and bloody. The Taliban have evolved their tactics to a devastating degree, retreating from the battlefield and using IEDs, or improvised explosive devises, and suicide bomb attacks.

According to the Marines' Brigadier General Larry Nicholson, Marjah will present "the largest IED threat NATO has ever faced".

IEDs are crudely made bombs, often detonated by remote control. Their strike rate is highly accurate and military intelligence officers say they are now claiming up to 90 percent of foreign troops' deaths and casualties.

Of the 57 foreign troops killed in Afghanistan so far this year, the vast majority have fallen to IEDs.

Operation Mushtarak comes after US President Barack Obama announced in December his plan for a troop surge to take the fight to the militants to clear the way for desperately needed governance and development.

The US and NATO are deploying an extra 40,000 troops, on top of the 113,000 already in Afghanistan, as part of the surge, with most heading to the southern battleground.

The Marjah assault is the spearhead of a new counter-insurgency strategy, brainchild of US General Stanley McChrystal, who commands foreign forces in Afghanistan, aimed at winning over ordinary Afghans to support the government.

He told a global security conference in Istanbul last week the situation in Afghanistan is serious but no longer deteriorating because "we have made significant progress... and we'll make new progress in 2010".

President Hamid Karzai is eager to bring on board Taliban foot soldiers, who largely fight for cash rather than loyalty to the Islamists, by offering them money and jobs to put down arms and rejoin mainstream society.

Marjah is at the heart of one of the world's biggest poppy growing areas. Illegal drug exports from Afghanistan are believed to be worth close to three billion dollars a year, helping fund the insurgency.

French army Major General Jacques Lechevalier said clearing the Taliban from the area would also add momentum to the fight against drugs and corruption.

"It's not just the jihadists and the Taliban, but also drugs and corruption that makes the bed of Islamism," he said.