Hardline Islamic politicians in Pakistan have reacted with outrage at the US bombing of a border area at the weekend, calling it a violation of sovereignty.

Pakistan's Government says the bomb was dropped on its territory during an operation by US troops in Afghanistan.

The US military says it took the action after a Pakistani border guard fired at a US patrol.

The guard was now in Pakistani custody, the US military said.

Qazi Hussain Ahmad, an MP of the Jamaat-i-Islami party, said mass protest rallies were being organised for Friday.

''The US bombing of Pakistani territory is an open violation of Pakistan's sovereignty," he said.

''The rallies will condemn this US interference."

The government's version of events contradicted US reports that the bomb had fallen inside Afghan territory.

School struck

Pakistani military spokesman Major-General Rashid Qureshi said: ''During an operation carried out by US troops in Afghanistan a bomb fell near the Durand Line in Pakistani territory."

There were no casualties or damage and Pakistan's military was investigating the incident, General Qureshi said.

North-west Frontier Province lawmakers condemned the attack

The US military in Afghanistan said one of its warplanes had dropped a bomb after a Pakistani border scout fired on a US patrol, injuring a US soldier, near the Afghan frontier town of Shkin on Sunday.

"One Pakistani border guard fired at coalition forces after being asked to retreat from the border", and then took cover in a nearby building, the US military said in a statement.

US forces then received gunfire from "several areas in the structure, leading them to assume there were more assailants", it said.

An F-16 airplane was called in to drop a bomb on the building - a disused school - but no one was hurt, it said.

The US military said the structure was inside Afghan territory, although it was 300 metres beyond a locally erected Pakistani guard post.

The region is regarded as a "grey area" in terms of border definition.

Strain on ties

Residents of the town of Angoor Adda in the Pakistani border district of South Waziristan said they saw two bombs fall on the empty religious school, destroying its outer wall.

Reports of the school being hit outraged legislators in the Islamist-ruled North-West Frontier Province, where anti-US feeling has run high since the American military campaign began in Afghanistan 14 months ago.

The provincial assembly passed a motion unanimously on Wednesday condemning the bombing as a violation of airspace and sovereignty.

The clash and bombing threaten to strain the crucial co-operation between US and Pakistani forces in flushing out militants who have escaped over the border into Pakistan.