KABUL - At least 45 civilians, many women and children, were killed in a rocket attack by the NATO-led foreign force in Afghanistan's southern Helmand province last week, a spokesman for the Afghan government said on Monday.

The incident happened in Helmand's Sangin district on Friday when civilians crammed into a mud-built house to flee fighting between NATO-led International Security Assistance Force (ISAF) troops and Taliban insurgents, Siyamak Herawi told Reuters.

"The investigation shows that the rocket was fired by NATO and 45 civilians, many of them women and children, have been killed," he said.

Civilian deaths and casualties caused by foreign troops are a major cause of friction between Afghan President Hamid Karzai and his Western backers and have led to street protests.

An ISAF statement late on Monday said a joint investigation with the government had so far found no evidence of civilian deaths.

"Any speculation at this point of an alleged civilian casualty in Rigi Village is completely unfounded," said ISAF Communication Director Rear Admiral Greg Smith in a statement.

"We are conducting a thorough joint investigation with our Afghan partners and will report any and all findings when known."

 CLASSIFIED DOCUMENTS LEAKED

Confirmation of the incident by the government comes on a day when tens of thousands of classified U.S. documents published by the whistleblower group WikiLeaks cast a new light on civilians caught in what it called "the true nature of this war".

The documents cover the period until U.S. President Barack Obama took office and adopted a new strategy that sought to reduce civilian deaths in conjunction with a troop surge to tackle the Taliban in their spiritual heartland.

ISAF casualties have soared this year but, after the new strategy's architect, General Stanley McChrystal, was dismissed in an insubordination scandal last month, his successor said he would review some operational tactics -- including air strikes on suspected Taliban hideouts.

In the worst incident of its kind, 140 civilians were killed in May last year in an ISAF air strike on a compound in Gerani, in western Farah province, among them 93 children and 25 women.

Western contributors to ISAF said reducing civilian casualties remained a priority.

"Our activities should aim first of all at defending the population, not fighting the population," Italian Foreign Minister Franco Frattini told reporters on the sidelines of a European Union meeting in Brussels on Monday.

"When civilian casualties occur, there is a very bad picture offered to public opinion and the world."

WikiLeaks said the documents it published on Monday showed thousands of civilian deaths, in ones and twos, went unreported or were unaccounted for.

The group's founder, Julian Assange, said the power of the material lay in its accumulation of small, previously unknown details rather than any disclosure of one large event.

"The real story of this material is that it is war, it is one damn thing after another. It is the continuous small events, the continuous deaths of children," Assange said.