Afghan forces drove Taliban militants out of the center of a district in the southern province of Helmand on Friday, as they fought back against insurgents who have threatened a series of districts over recent months.

Deputy Interior Minister Ayoub Salangi said security forces had retaken the district of Khanishin in the south of Helmand, after it fell to the Taliban this month.

"The district of Khanishin is cleared of enemies and Afghan forces inflicted heavy casualties," Salangi said.

Helmand, a traditional stronghold of the Taliban and one of the biggest centers of opium production, has been the scene of fierce fighting over recent months as the militants have pressed their insurgency following the withdrawal of most international forces last year.

The Taliban have been seeking to build on last September's brief capture of the northern city of Kunduz, their biggest success since they were driven from power by a U.S.-led intervention in 2001.

The fighting in Helmand has carried echoes of the campaign that led to the fall of Kunduz, when Taliban fighters established themselves in the surrounding district before moving on the city itself.

In Helmand, where the insurgents have threatened the provincial capital, Lashkar Gah, they have already seized the districts of Musa Qal'ah and Now Zad in the north of the province before taking Khanishin last week.

Since then, they have come close to taking the district of Marjah, about 35 km (21 miles) from Lashkar Gah, and the focus of a major offensive by U.S.-led NATO troops in 2010.

Afghan police and army units have complained bitterly that they have received inadequate support and supplies from the government in Kabul and suffered high rates of desertion.

International partners have looked on with mounting alarm.

The New York Times reported this week that U.S. special forces had taken part in fighting in Helmand, a rare venture into active combat that underlined the gravity of the situation facing government forces.

The report has not been confirmed by NATO headquarters in Kabul.