HEART: Afghans chanted "Death to America" and demanded US troops leave Afghanistan as mobs threw stones at government offices Thursday in a violent protest against civilian deaths, witnesses said.

Four people were wounded when hundreds of furious demonstrators protested in the western town of Farah against the reported killings of up to 70 civilians during US-led air strikes and fighting against insurgents, officials said.

"Police tried to disperse them but they started throwing stones at police, who fired into the air," deputy provincial governor Mohammad Younus Rasouli told AFP, describing the protest as "violent."

He said no one was hurt in the shooting. However, the provincial health director, Abdul Jabar Sahieq, said one demonstrator was admitted to hospital with gunshot wounds and three others with injuries from being trampled.

"People are really angry and they shout 'death to America, death to the invaders,'" a demonstrator who gave his name only as Abdullah told AFP before the protest was broken up.

"They are hurling stones at government buildings and there is some gunfire in the air," he said, adding that he did not know who was firing.

US military and Afghan teams pressed ahead Thursday with an investigation into how many civilians and insurgents were killed in fighting and air strikes this week, in what may have been one of the deadliest incidents for Afghan civilians in eight years.

Afghan police said more than 100 people were dead, most of them civilians. One Afghan official said he had seen the bodies of 20 children.

Haji Nangyalai, 42, said he was demonstrating to "show our anger at the crimes committed by the American forces."

"We ask the Afghan government to force the American forces to leave Afghanistan. They kill more civilians than the Taliban," he said angrily.

The United States has around 38,000 troops in Afghanistan, the bulk of a foreign deployment of roughly 70,000 tasked with hunting down armed Islamist extremists and stabilising the country.

The killing of civilians in foreign military operations is a sore point between Washington and Kabul, which warns it is squandering local support for the gruelling fight against a vicious, Taliban-led insurgency.

A delegation of foreign troops and Afghan government officials left for Bala Buluk district, about 50 kilometres (30 miles) north of the provincial capital, earlier in the day to continue investigations, police said.

The police spokesman for western Afghanistan, Abdul Rauf Ahmadi, told AFP Wednesday that, according to information passed to him, up to 30 of more than 100 people who died in the air strikes and ground operations were Taliban.

The remainder were civilians, including children, women and elderly people, he said.

In the nearly eight years since the US military invaded Afghanistan to oust the Taliban and remained to fight the insurgency, civilians have been reported killed in multiple strikes against militants.

If investigators confirm 70 non-combatants were killed in Bala Buluk, it would make it the deadliest such incident affecting civilians in Afghanistan.

US military spokesman Colonel Greg Julian told AFP, however, that investigators were looking into claims that some of the civilians may have been killed by the Taliban and not in the air strikes.

Last year was the most dangerous for civilians caught up in the conflict, according to UN figures that estimate nearly 2,200 were killed, about 55 percent in insurgent attacks and nearly 40 percent by pro-government forces.

The NATO-led force announced, meanwhile, that an investigation had concluded that two civilians were killed and two wounded in an April 27 air strike against insurgents in the southern province