"In all, the investigation team estimates that 60-65 Taliban extremists were killed in these engagements, while at least 20-30 civilians may have been killed during the fighting," a US military statement said.

The Afghan government said on Saturday that an investigation concluded at least 140 civilians died in the US air raids.

The US military said its investigators could not conclusively determine the number of people killed in the fighting.

Raids by US fighters aircraft had targeted buildings where suspected Taliban fighters were regrouping after a series of clashes, it said.

The death toll presented by the Afghan authorities would make the Bala Buluk clashes the deadliest incident for Afghan civilians since the US-led invasion in 2001.

The US military had previously acknowledged that "a number" of civilians were killed, but said it was impossible to say how many because all the bodies were buried before investigators arrived.

University students have rallied in the Afghan capital, Kabul, angered by the deaths of more than 125 villagers in a US air raid.

The students took to the streets on Sunday, saying they held the US responsible for the killings in Farah province  and demanding that those who ordered the air raids be put on trial.

During the protest outside Kabul University, a student leader read out a statement saying: "Our people are fed up with Taliban beheadings and suicide
bombings.

"On the other hand, the massacre of civilians by the American forces is a crime that our people will never forget."

Members of the crowd yelled "Death to the biggest terrorist" and "long live Islam".

It is the second demonstration since the Farah province assault last Monday.

A demonstration in the provincial capital, also called Farah, on Thursday turned violent as protesters threw stones and police fired shots.

The killings are said to be the largest single loss of civilian life since US-led forces entered Afghanistan to overthrow the Taliban rulers of Kabul.

A joint investigation by the US military and Afghan forces has acknowledged that "a number" of civilians died in the incident, but is yet to give a full account of what happened.

Hamid Karzai, the Afghan president, is under increasing pressure over the US military presence in the country, and over deadly aerial bombardments in particular.

On Saturday, he repeated his call for the US to end air strikes.

The US has apologised in the past for civilian deaths due to air raids and has promised to take measures to avoid a repeat of the loss of life.

Manned attack

The US military statement came on the same day that two Americans, including a soldier, were killed in an suicide bomb attack on a US military convoy near Kabul, the Afghan capital, according to officials.

The convoy was travelling between the US air base at Bagram and the north of Kabul when it was hit on Wednesday.

One American soldier and a US civilian working for the military were killed, an US military official said.

Violence in Afghanistan is at its highest level since a US-led coalition forced the Taliban out of power in 2002.

Barack Obama, the US president, has promised to address Afghanistan's long-term stability during his time as commander-in-chief, pledging thousands more US troops to the country.

Khalilzad denial

In another development, Zalmay Khalilzad, a former US ambassador to the UN and Afghanistan, has denied reports that he is not looking for a post in the Afghan government.

The New York Times newspaper quoted diplomats and US officials on Tuesday as saying that Hamid Karzai, the Afghan president, mentioned the idea of a high-level position in the Afghan government for Khalilzad during recent meetings with senior aides to President Barack Obama.

Khalilzad said he had not left the US since Karzai was in Washington earlier this month. "Obviously I care about Afghanistan," he told The Associated Press news agency.

"I've always said that I would help. That shouldn't be taken that I was a candidate for president or a candidate for the CEO job.

"I am not looking for a job for myself in the government of Afghanistan. I'm not negotiating with Karzai for a position for CEO."