Suspected US troops kill 20 in Pakistan attack

The attack is likely to spark uproar in Pakistan where it is will be seen as undermining sovereignty at a time when a new civilian Government is struggling to assert authority in the turbulent nuclear-armed state.

"It is outrageous," Owais Ahmed Ghani, governor of North West Frontier province, said in a statement.

"This is a direct assault on the sovereignty of Pakistan and the people of Pakistan expect that the armed forces would rise to defend the sovereignty of the country and give a befitting reply," he said.

A spokeswoman or Afghanistan's NATO-led force said she had no information about the incident.

A spokesman for a separate US-led coalition force declined to comment, referring questions to the US Central Command.

The United States says al-Qaeda and Taliban militants are based in sanctuaries in northwest Pakistan's ethnic Pashtun tribal areas on the Afghan border, where they orchestrate attacks in Afghanistan and Pakistan and plot violence in the West.

There were differing accounts of the attack with some people saying it was carried out by helicopter gunships while others spoke of an attack by ground troops as well.

"Troops came in helicopters and carried out action in three houses," said Gul Nawaz, a shopkeeper in the village.

Other residents said the foreign troops detained some people and took them away.

US-operated pilot less drone aircraft have launched attacks in Pakistani border regions several times in 2008, killing dozens of militants, but US ground troops had not been known to cross into Pakistan to fight militants.

Pakistan is a staunch US ally, even though the campaign against militancy is deeply unpopular with many people, but it rules out any encroachment by foreign soldiers onto its territory.

Pakistani Defence Minister Ahmed Mukhtar said aircraft belonging to foreign forces in Afghanistan attacked three houses at 4.30 am.

He declined to comment further, saying the Foreign Ministry was investigating.