US-controlled Predator aircraft have struck several sites used by al Qaeda operatives in Pakistan this year, most recently on Thursday when four low-level al-Qaeda-linked militants were killed in the same region, security officials said.

The Friday attack was on a house in the Guvrek area, near the border with Afghanistan.

"Two drones were flying in the area. They fired three missiles," said a witness who declined to be identified.

An intelligence official said five militants were killed while another said the the toll could rise. It was not immediately known if any senior al-Qaeda figures were among the casualties.

Military spokesman Major-General Athar Abbas said they were checking reports of the attack.

On Wednesday, US forces carried out a pre-dawn helicopter-borne ground assault on the village of Angor Adda in the nearby South Waziristan in the first known incursion into Pakistan by US-led troops since the 2001 invasion of Afghanistan.

Officials said 20 people, including women and children, were killed in the attack which sparked fury in Pakistan.

Pakistan is a staunch ally in the US-led war on terrorism but rules out encroachment by foreign troops onto its terrority.

Pakistan condemned the Wednesday attack and summoned the US ambassador to lodge a protest. Parliament called for border raids to be repulsed.

The anger over US attacks comes in the run-up to a Presidential election.

Asif Ali Zardari, widower of assassinated former Prime Minister Benazir Bhutto, looks set to become president on Saturday in an election by legislators to chose a replacement for Pervez Musharraf, who resigned last month.

Zardari is seen as close to the United States but the anger over US strikes is not expected to hurt his chances of victory.

However, ordinary Pakistanis, many of whom harbour anti-American feelings, will be expecting him to take a stand against the US attacks.