LASHKAR GAH: Dozens of Afghan soldiers and policemen have been killed in the southern province of Helmand since Sunday as the Taliban presses an in one of its heartlands, officials said.

Three local officials, who all spoke on condition of anonymity because they have been ordered not to talk about casualty figures, said 25 soldiers and 27 policemen had been killed in separate incidents in the province.

Afghan security forces, fighting largely alone since the withdrawal of international forces in 2014, have been struggling for months to hold back the insurgency in Helmand, where the Taliban inflicted hundreds of casualties on Nato troops during years of fighting.

At least 11,000 civilians were killed or wounded in Afghanistan last year, in the worst year for civilian casualties since the United Nations began keeping records in 2009. Heavy fighting over the winter points to the potential for even more bloodshed this year.

As well as the fighting in Helmand, Taliban operations in the northern provinces of Jowzjan, Kunduz and Baghlan have also severely stretched government forces and caused heavy casualties over recent days.

In the worst incident in Helmand this week, insurgents in captured military Humvee vehicles packed with explosives launched a suicide attack on a checkpoint in the district centre of Sangin on Sunday, killing seven soldiers and 15 policemen.

Nine soldiers were also killed in combat in Sangin, while another nine died in fighting in Musa Qalah district, northeast of Sangin, the officials said.

In other incidents, 10 policemen were killed fighting in Gereshk, a road junction north of the district capital Lashkar Gah, while two more were killed on Monday night in Khan Nashim in the south of the province by a man wearing a police uniform.

The Taliban, which the United States now estimates controls or threatens around a third of the country, have overrun large parts of Helmand, leaving beleagured government forces in district centres like Sangin and Marjah barely clinging on to a few official buildings.

Heavily mined roads have prevented reinforcements and supplies arriving, leaving many units cut off.

“Right now, some 250 police and 300 soldiers are surrounded by Taliban in Marjah and our forces are providing them support from the air,” one of the officials said. “Roads to Sangin are mostly blocked with explosive devices and we cannot send reinforcements.”

The outgoing US commander in Afghanistan, Gen. John Campbell, recently ordered several hundred American troops to the province to bolster the defence, although they will be restricted to an advisory role unless they come under attack themselves.