NATO warplanes killed at least 50 civilians, mostly women and children, in bombing in southern Afghanistan during a major Islamic holiday, local leaders said yesterday.

The incident happened on Tuesday, the middle of the Eid al-Fitr festival marking the end of the Muslim fasting month, in Panjwai, an area where the alliance said it had killed hundreds of insurgents in a two-week offensive last month.

NATO says it killed 48 insurgents during heavy fighting in the area in Kandahar Province on Tuesday and had received credible reports that several civilians were killed in the operation.

The defence ministry has sent a team to investigate.

"It was late at night that might be the reason they didn't know where to bomb," said provincial assembly member Agha Lalai. "They have bombed residential houses."

Visiting the wounded in hospital, tribal elder Naik Mohammad said 60 civilians had died. Villagers also said 60 died and another member of the provincial assembly put the toll at 80.

Witnesses say 25 homes were razed in 4-5 hours of bombing.

The United Nations mission in Afghanistan, UNAMA, yesterday urged a speedy and thorough investigation.

"The United Nations Assistance Mission in Afghanistan is very concerned by reports that a great number of civilians may have died during the conduct of military operations," it said in a statement in Kabul.

"The safety and welfare of civilians must always come first and any civilian casualties are unacceptable, without exception."

This is Afghanistan's bloodiest year since the Taliban's Islamist government was ousted in a US-led invasion in 2001.

More than 3,000 people have been killed, mainly militants but including many civilians and more than 150 foreign soldiers.

The Taliban and other militants have regrouped, helped by a booming illegal opium trade and growing frustration at the slow pace of reconstruction and a lack of jobs or a real economy.

NATO's commander in Afghanistan, British General David Richards, has warned the next six months will be pivotal, saying Afghans could turn to the Taliban if they did not see promised development delivered.

In a message to Afghans, Taliban chief Mullah Mohammad Omar vowed to step up attacks and a senior guerrilla has told the BBC the group will increasingly use suicide bombers up to six in a single attack.

"So far you see just individual suicide attacks, but in the future you might see as many as six people committing the attacks simultaneously," Hajji Mullah Wahid Ullah, described as a Taliban adviser, told the BBC. "Countless people have enlisted to become suicide bombers. This upsurge is the result of the pressure we are under."

Recent Taliban footage obtained by Reuters shows several suicide bombers pledging to die to drive out "foreign infidels."

Although still not as common as in Iraq, suicide bombings have increased dramatically this year, killing more than 200 people so far compared with 50-60 through all of 2005.

Editor: Yan