British Prime Minister Gordon Brown paid a surprise visit to Musah Qalah in Helmand, a heartland province of Afghanistan said to be the Taliban's last key stronghold in the embattled country.

Brown was on his way from Basra in Iraq to the Afghan capital Kabul, where he held talks with his counterpart Hamid Karzai.

"I know the work you are doing today and over the next few days is important to the whole mission in Afghanistan. I believe, if we can succeed there, which we will, we can move forward to a more peaceful future for this country," Brown told British troops.

Brown and Karzai held a press conference, where Brown proclaimed the coalition offence in Musa Qalah as a success.

"This action in Musah Qalah is an example of how Afghanistan forces working with British can make a difference," CNN reported Brown as saying.

International forces, along with Afghan troops, launched a major offensive in the opium-rich region in and around Musa Qalah, which fell into Taliban hands in February after the coalition had left the region in control of tribal elders.

An International Security Assistance Force spokesman said that Afghan army troops entered the centre of Musa Qala on the fourth day of operations to recapture it, but fighting continued. Meanwhile, an Afghan defence ministry spokesman said that coalition forces had 'completely captured' the town.

The North American Treaty Organisation said that on Sunday, coalition forces had succeeded in capturing 10 Taliban militants and killing several others.

Combined Afghan and British forces were searching compounds for people connected with an arms dealer who was killed in an earlier air strike when they detained the 10 militants.

Many other militants, who attacked the troops with small arms, were killed. Two teenaged boys were wounded in an air strike, and were taken to a medical facility for treatment, the ISAF said.

The British defence ministry said Afghan troops were leading operations on the ground, whereas British and United States forces provided additional support on the ground and in the air.

"It is going according to plan. As to how tough the fighting will be or will not be, that's up to the insurgents," General Dan McNeill, ISAF's American commander, told CNN.

"The Afghan government has long said that it would retake Musa Qalah from the scourge of the Taliban when the time is right. The time is now right," British Defence Minister Des Browne was quoted as saying.

Since Afghan and ISAF forces began operations in Helmand in November, they have made significant progress in Gereshk and Sangin, the British defense ministry said.

The operation in Musa Qala is one of the largest against the Taliban since the invasion in 2001. It was launched after weeks of air strikes and probing attacks, which had softened up their defences and killed hundreds of their fighters.

The final push into the town, which would largely entail house-to-house fighting, will be made by the Afghan army supported by British troops.