Nato-led troops have killed three Afghan children and injured seven during artillery fire in Afghanistan's eastern province of Paktika.

Nato officials said that the attack on Monday happened by accident.

The deaths in Paktika province are expected to deepen the rift between foreign forces and the Afghan government.

The Afghan government has said that more than 500 civilians have been killed during operations by foreign and Afghan forces this year.

'Investigation under way'

In the latest incident, troops fired artillery rounds after a patrol came under fire from Taliban fighters in Paktika's Gayan district, Nato's International Security Assistance Force (Isaf) said.

The rounds fell close to a house where the children were later found dead.

"ISAF deeply regrets this accident and an investigation as to the exact circumstances of this tragic event is now under way," the ISAF said in a statement.

Dad Mohammad Khan, a former provincial intelligence chief and politician, said: "There is basically no Taliban [killed]. The Taliban fire and then escape and then these people [foreign troops] come and bombard. Three hundred people have been killed and wounded".

The incident came hours after the US-led coalition command said its troops killed more than 220 fighters in a week of fighting in the same province. The coalition did not say where the militants were killed.

Fuelling anger

Meanwhile in Kabul, Afghanistan’s capital, hundreds of protesters blocked a road, accusing foreign troops of killing a family of four, including two children.

The family members were killed in an overnight raid by international troops, a police official and witnesses said.

Residents in Hud Kheil in the east of Kabul said one of the two children was eight months old and grenades killed the family members during a joint Afghan-US special forces operation.

However, US special forces said they were not involved.

"It was past one o'clock when the troops came and surrounded our houses," Sulaiman, one resident, said.

"They threw hand grenades in one house and killed three family members," he said.

Some locals told Al Jazeera there was an exchange of fire and that the family may have been caught in the crossfire.

The latest deaths are likely to further strain relations between Afghanistan and the US and other foreign forces in the country, who have been accused of using excessive force in civilian areas.

The operation came a day after Nato said it received information from a "reliable source" that pro-Taliban fighters may be planning to falsely claim that international forces killed up to 70 civilians in southern Afghanistan.

The operation also comes after Hamid Karzai, Afghanistan's president, sacked an Afghan army general and a major after more than 100 civilians were reported to have been killed in an attack by US-led coalition forces.

Violence in Afghanistan is at its worst level this year, the bloodiest period since the Taliban was forced from power in 2001.