U.S. officials say a drone strike in northwestern Pakistan has killed al-Qaida's second in command, Abu Yahya al-Libi, dealing what is said to be a major blow to the terror group.

Tuesday's confirmation of al-Libi's death came a day after missiles from a U.S. drone hit a vehicle and compound in the North Waziristan tribal region, killing at least 15 people, including foreigners.

A Pakistani official said authorities had intercepted a telephone conversation in which militants talked about the death of an Arab, and residents in the area had said they believed al-Libi was in the compound at the time of the strike. The senior al-Qaida leader was reportedly wounded in a U.S. drone strike in North Waziristan on May 28.

The latest drone strike was the third since Saturday — with a total of at least 27 people killed.

Pakistan's foreign ministry on Tuesday summoned Deputy U.S. Ambassador Richard Hoagland to convey “serious concern regarding drone strikes in Pakistani territory.” The ministry called the strikes “unlawful, against international law and a violation of Pakistan's sovereignty,” and a “red-line” for the country. It also noted that Pakistan's parliament had “emphatically stated” that drone strikes are “unacceptable.”

Christopher Snedden, a South Asia analyst with the Melbourne-based security consultancy Asia Calling, told VOA the United States is likely to continue the drone strikes because they are an effective way to go after militants without endangering U.S. forces.

“I expect that they will do that because it's such an efficient way of running an operation. It may be reduced if Islamabad and Washington can actually improve their relationship but there's nothing in the short term that suggests that's going to happen.”

The Libyan-born Libi has been running al-Qaida's day-to-day operations in Pakistan's tribal regions as well as its links to regional affiliates. He escaped prison at Bagram Air Base in Afghanistan in 2005 and appeared in a series of propaganda videos before rising to become the terror group's deputy leader last year. The U.S. government had placed a $1 million price on his head.

At the Pentagon, spokesman John Kirby refused to provide reporters with details of counterterrorism operations. But he said al-Libi is a “very dangerous individual, and for him to no longer be walking the earth would be a good thing for everybody.”

The Pentagon spokesman also said U.S. Defense Secretary Leon Panetta has made it very clear that the United States will deal with threats to the security of the United States and its allies “wherever they are.”

Relations between Washington and Islamabad have reached a new low following last year's killing of al-Qaida leader Osama bin Laden in Pakistan by U.S. special forces and the accidental killing of 24 Pakistani soldiers in a NATO air strike.

Pakistan's parliament has demanded a U.S. apology for the deadly cross-border attack last November and an end to the U.S. drone strikes. Washington refused to end the missions, saying drone strikes are a vital tool in the war against al-Qaida and the Taliban. Islamabad responded by blocking NATO supply routes into Afghanistan and the two sides have yet to reach an agreement on reopening them.

Senior U.S. defense official Peter Lavoy is set to hold talks with Pakistani officials in Islamabad this week to try and break the deadlock over the supply routes.