At least 11 Afghan soldiers have been killed in a Taliban ambush in western Afghanistan, officials said Monday, as troops face their first fighting season without NATO combat support.

The militants launched their annual spring-summer offensive in late April, vowing nationwide attacks in what is expected to be the bloodiest summer for a decade.

Afghan troops and police, stretched on multiple fronts and facing record casualties, are struggling to rein in the militants even as the government makes repeated efforts to jump-start peace negotiations.

"The Taliban ambushed a convoy of soldiers in Karukh district of Herat, killing 11 Afghan army soldiers last evening. The soldiers were riding in pickup trucks," Ehsanullah Hayat, spokesman for the governor of the western province of Herat, told AFP.

Najibullah Najibi, a spokesman for the army in western Afghanistan, confirmed the attack and said four soldiers were wounded.

The Taliban have stepped up their attacks on Afghan security forces since the start of their spring offensive, named "Azm" (Determination) this year.

NATO’s combat mission formally ended in December after 13 years, but a small follow-up foreign force named Resolute Support has stayed on to train and support local security forces.

In a separate incident dozens of protesters took to the streets in Charikar, the capital of Parwan province north of Kabul, on Monday to complain about an operation by foreign forces overnight.

They were unhappy that a house was raided and an ammunition cache destroyed in the Bayaan district of the province.

The NATO mission confirmed the operation by US forces.

Its aim was "to destroy a cache of munitions that could be used to conduct attacks against Afghans and coalition forces", a spokesman told AFP.

Protesters set tyres on fire in the main market and chanted anti-American slogans, according to local TV reports.

"The people got angry because they (foreign forces) detonated the cache at midnight while they were sleeping," said provincial police chief General Mohammad Zaman Mamoozai.

Story continues

He said the cache dated back to the struggle against the Soviet occupation in the 1980s, complaining that local authorities were not warned about the raid which caused no casualties.

Interior ministry spokesman Sediq Sediqqi said police were investigating the incident.

Abdullah Abdullah, the government's chief executive, called for calm and said he was in contact with General John Campbell, the commander of NATO forces in Afghanistan, about the issue.

Night raids and house searches by foreign forces in their battle against the Taliban were one of the most controversial issues in the time of former President Hamid Karzai, often causing disputes between Washington and Kabul.

Such operations are traditionally opposed by many Afghans, especially in conservative rural areas, where people see them as an "invasion" of their families and women.

Parwan is home to Bagram airfield, the biggest foreign forces base in Afghanistan that often comes under Taliban rocket attack from nearby villages.