Afghan forces have spent months trying to keep the Taliban at bay.
The Taliban have captured the crucial southern Afghan city of Sangin after a year-long battle, officials say.
Afghan forces say they have made a tactical retreat from the centre of Sangin.
A spokesman for Helmand’s governor confirmed the district police and governor’s headquarters were now in militant hands.
Almost a quarter of British troops killed during the UK’s combat mission in Afghanistan died defending Sangin.