Afghan civilians trying to flee a firefight in which 40 people died -- many of them reportedly wedding guests -- were stopped from getting to safety by insurgents, US forces said.

The international coalition said nine insurgents were killed in a battle in the southern province of Kandahar but could not confirm civilian casualties, although it was investigating, US Forces Afghanistan said in a statement.

President Hamid Karzai said in a statement late Wednesday that around 40 civilians, including women and children, were killed and about 28 wounded in what villagers in Wocha Bakhta, 80 kilometres (50 miles) north of Kandahar, said was a wedding party.

The high number of civilian casualties in military operations has caused friction between Kabul and its international allies.

However, international forces, which have tens of thousands of troops here trying to put down a Taliban-led insurgency, say insurgents do little to try to protect non-combatants.

`Witnesses reported seeing insurgents firing machine guns, rockets and RPGs (rocket propelled grenades) from the rooftops of buildings in the area, as well as mortar teams firing around the ambush site,` US forces said.

`Civilians reportedly attempted to leave the area, but the insurgents forced them to remain as they continued to fire on the ANSF (Afghan National Security Forces) and coalition forces along the highway.`

Police had said that villagers were hurt as they tried to leave the area but it was unclear how they had been wounded, the statement added.