U.S. drone strikes in Pakistan said to kill 2 top Al Qaeda leaders ISLAMABAD, Pakistan - Recent U.S. drone missile strikes in northwest Pakistan have killed two Al Qaeda commanders, according to Pakistani intelligence sources, including a militant leader who had replaced Al Qaeda's second-in-command, Abu Yahya al Libi, killed by a drone missile this summer. The sources said Sunday that Abu Zaid al Kuwaiti, a senior Al Qaeda leader who had replaced Al Libi, was killed in a drone strike Thursday near the town of Mir Ali in North Waziristan, the tribal region along the Afghan border that has long served as a stronghold for an array of militant groups, including Al Qaeda commanders, the Afghan Taliban wing known as the Haqqani network, and the Pakistani Taliban. Al Libi became Al Qaeda leader Ayman Zawahiri's top deputy following the May 2011 U.S. commando raid that killed Osama bin Laden in the Pakistani city of Abbottabad. Al Libi was killed in a drone strike in Pakistan's tribal belt in June. On Sunday, a drone missile strike near the North Waziristan town of Ghulam Khan killed Muhammad Ahmad al Mansoor, a senior Al Qaeda commander, and three Pakistani militants, Pakistani intelligence sources said. Washington has opted to continue its drone campaign against Al Qaeda and Taliban militants in the tribal belt along the Afghan border despite repeated calls from Islamabad to abandon the tactic. Though the U.S. use of drones remains a major source of friction between Washington and Islamabad, relations between the two countries have been steadily improving - a stark contrast from a year ago when the tenuous alliance came to a near-standstill. In 2011, a series of events enraged Pakistan and prompted it to pull back its level of cooperation with the U.S. Those included the shooting deaths of two Pakistanis by a CIA contractor, the U.S. commando mission that slipped into Abbottabad and killed bin Laden, and errant U.S. helicopter airstrikes along the Afghan border that killed two dozen Pakistani soldiers. The deaths of the soldiers prompted Pakistan to shut down for seven months transit routes through the country that the U.S. and NATO uses to supply its soldiers battling Taliban militants in Afghanistan. The number of U.S drone strikes in Pakistan has dropped sharply in the last two years. In 2010, there were 117 U.S. drone strikes against Al Qaeda and Taliban militants in Pakistan's tribal areas, according to the Long War Journal, a website that tracks U.S. drone activity. In 2011, the number dropped to 64, and so far this year, there have been 44 drone strikes. Still, Washington regards drones as a valuable tactic against Islamic militant leaders and their strongholds in Pakistan's tribal region, and has shown no signs of abandoning their use altogether. Pakistan argues that drone missile strikes are a blatant violation of the country's sovereignty, and that they effectively fuel militancy by creating new recruits for militant groups out of tribesmen angered by the deaths civilians killed in the strikes. Suicide bombing planned in Pakistan, Afghan leader says 'Smaller piece of the pie' for workers worldwide, report says Staff writer Alex Rodriguez reported from Islamabad, and special correspondent Zulfiqar Ali reported from Peshawar.