A "substantial" Taliban force stormed the small town of Musa Qala in the southern province of Helmand late Thursday, disarming police and occupying the administration headquarters, the Nato-led International Security Assistance Force (Isaf) said.

The situation in the remote district, also called Musa Qala, was unclear but "we have indications that Taliban are fortifying their positions in the district centre," spokesman Colonel Thomas Collins said.

"We know there are fighters in the area but to the extent, I can't give you real details.... I can't give you a clear idea of what the nature of their control is in the town in this time," he told AFP.

"They control a small area but to say they control the entire district is going too far."

The defence ministry confirmed that the police and administration structures in the town had been disbanded. "It is under Taliban control since yesterday," ministry spokesman General Zahir Azimi told AFP.

An ISAF statement late Friday said there were reports that "an unknown number of Taliban have entered the Musa Qala district centre in Helmand province, that pressure has been placed on the elders and the Afghan national flag has been taken down."

Provincial governor Asadullah Wafa said Friday civilians were fleeing the town fearing imminent Isaf and Afghan army strikes to drive out the Taliban.

Collins said Isaf was ready to support government forces preparing to retake the centre.

"We are confident it will come under full government of Afghanistan control," he said. "The Taliban have in the past seized district centres and held them for some hours or days but they are eventually run out."

The extremist Taliban movement, which was in government between 1996 and 2001, last year briefly took control of a handful of centres in remote parts of southern Afghanistan before being ejected by military forces.

The British military, which has the bulk if its deployment of 6,000 troops to Afghanistan in Helmand, in September withdrew its forces five kilometres (three miles) from Musa Qala town at the request of the government after tribal leaders said they would see the peace was kept.

Isaf, which did not negotiate with the extremists, said the deal was potentially a "local solution" to the Taliban-linked unrest blighting the area, but critics said it could provide the militants with a sanctuary.

Collins rejected allegations the tribal leaders may have been in cahoots with the Taliban when reaching the agreement.

If they had, the Taliban would not have had to enter the town with armed forces. "They took the tribal elders into custody for a while, they threatened them. Obviously they were not getting their way," he said.

Collins also rejected media reports that US forces unhappy with the deal were planning to enter Musa Qala town in the coming days, with US General Dan McNeill due on Sunday to take over command of Isaf from a British general.

Wafa, appointed provincial governor in December -- about two months after the deal was struck, is among the critics. "Even from the beginning I said this is not going to work," he said Friday.

Helmand produces about a quarter of Afghanistan's illegal opium crop, which makes up more than 90 percent of the world supply. There is suspected Taliban involvement in the industry.

In 2006 the province saw some of the fiercest fighting in the Taliban-led insurgency, which was its most violent last year. More than 4,000 people were killed across Afghanistan -- most of them rebel fighters.