A spokeswoman for the Nato-led ISAF force had confirmed to Al Jazeera on Tuesday that the centre of Washir, a remote desert area in the northwest of Helmand, was in the hands of the Taliban.
She also said that the town would be brought back under government control.
In recent days, thousands of residents have fled from Musa Qala, a town in southern Afghanistan, while Taliban fighters who moved in last week consolidated their positions.
Haji Assadullah Wafa, the governor of Helmand province, told Reuters that a military operation to recapture Musa Qala would be launched soon.
"The Taliban are only in the town to create problems for the people," the governor said.
"They do not have the ability to seize an area and maintain their control over it."
British-led Nato troops withdrew from the town after striking a deal with local authorities and tribal elders in October.
The agreement meant that Nato troops and Taliban fighters were not supposed to come within 5km of the town centre, but a group of 200 Taliban disarmed the local police force, destroyed the district centre and temporarily held local elders hostage.
The Taliban made their move after accusing Nato of violating the deal during an air strike that killed the brother of Mullah Ghafour, a local Taliban leader.
Nato commanders and tribal elders have said that the attack was outside the area covered by the truce.