Kabul, Afghanistan (CNN) After several days of fierce fighting, Taliban forces have taken almost full control of Sangin, a key district in Afghanistan's southern Helmand province, a police official said.

The Taliban took over the entire district except for the police chief's compound and another compound where a battalion of Afghan National Army is based in, said Mohammad Dawood, the Sangin police chief.

December marks one year since NATO handed over security operations to the Afghans. Before then, British and American forces struggled for years to hold on to Sangin.

It is strategically important because it links Lashkar Gah, the Helmand capital, to districts in the north. If the Taliban gain control of Sangin, they will control supply routes to the districts.

Dawood said the fighting in the district had been going on for more than a month, but was in its worst stage in the past three days.

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