Three top Al Qaeda [Images] leaders were among 21 people killed in a missile strike by a US drone on a madrassa in Pakistan's restive North Waziristan tribal region on Monday.

Security officials were quoted by Dawn News channel late on Monday night as saying that Al Qaeda leaders Hamza Arabi, Qasim Hamza and Musa Arabi were among those killed in the attack on the seminary in Tanda Darpakhel, two km from Miranshah, the headquarters of North Waziristan.

Women and children were also among the dead. Twenty others were injured in the missile strike.

The drone operated by US-led forces in Afghanistan fired six to seven guided missiles. Four missiles hit a madrassa run by senior Taliban [Images] leader Jalaluddin Haqqani while three hit nearby houses.

State-run APP news agency quoted official sources and local residents as saying that three female seminary students and three labourers were among the dead.

It was not immediately known if Haqqani was present in the area at the time of the strike. Haqqani, a close aide of Taliban supreme commander Mullah Omar, has not been seen since the fall of the Taliban regime in Kabul in 2001.

ARY News channel reported that Naseeruddin Haqqani, the son of Jalaluddin Haqqani, had said his father and brother Sirajuddin were "alive and well" in Afghanistan.

Taliban fighters surrounded the area around the madrassa and did not allow people to approach the site. North and South Waziristan tribal regions are considered strongholds of the Pakistani Taliban led by Baitullah Mehsud.

Since last week, Pakistan's tribal belt has witnessed a sharp increase in attacks by drones operated by US-led coalition forces in Afghanistan. More than 40 people have died in these strikes.

Twenty people, a majority of them women and children, were killed in a raid in South Waziristan by gunship helicopters and commandos of the coalition forces on September 3. That attack marked the first time that US-led ground forces from Afghanistan had intruded into Pakistan.

Pakistan has angrily condemned the attacks as a violation of its sovereignty.

The US has accused Jalaluddin Haqqani of organising some of the most serious attacks against coalition forces in Afghanistan and of masterminding a failed assassination attempt on Afghan President Hamid Karzai [Images].

The Haqqanis, they say, also protect Al Qaeda elements in their bases in North and South Waziristan and act as a link between Afghan and Pakistani Taliban.