- Investigators are trying to determine whether Abu Yahya al-Libi was killed in the strike
- The militant is a Libyan and a prominent al Qaeda face on the internet
- The drone strike, in North Waziristan, was the 21st in Pakistan this year
- The strikes have degraded the top ranks of al Qaeda
(CNN) -- Abu Yahya al-Libi, the no. 2 man in al Qaeda and a longtime public face of the terror network, has been targeted by a drone strike in Pakistan's tribal region, a U.S. official said Tuesday.
Investigators are trying to determine whether al-Libi was injured or killed in the Monday hit, which left 15 militants dead and three others wounded, the official said. Intelligence officials may find out al-Libi's fate only from monitoring websites and chatter, according to the official.
A senior Pakistani official said investigators have to verify that al-Libi was among the dead. Eight of the victims from the strike were "foreigners," with most of them Arabs, the Pakistani official said.
The drone fired at least six missiles at a militant compound near the town of Mir Ali in the North Waziristan region near the Afghanistan border.
It was the third such deadly attack in as many days and the 21st suspected U.S. drone strike in Pakistan this year in the fight against al Qaeda.
Al-Libi was elevated to No. 2 in the terror organization after U.S. Navy Seals killed al Qaeda leader Osama bin Laden last year and Ayman al-Zawahiri became the group's leader.
Al Qaeda's leadership has been so thinned by the U.S. drone campaign in Pakistan that these men are the only two real leaders of the organization left, U.S. counterterrorism officials said, according to CNN Security Analyst Peter Bergen.
An Islamic scholar and high-ranking member of the group, al-Libi frequently appears in Internet videos. He has given many videotaped speeches praising al Qaeda leaders, urging resistance and trying to recruit new members.
"Al-Libi is a key motivator in the global jihadi movement and his messages convey a clear threat to U.S. persons or property worldwide," said a "Wanted" statement posted on the website of the U.S. State Department's "Rewards for Justice" program, which offers rewards for information on suspected terrorists.
"Al-Libi is believed to be in hiding in Afghanistan or Pakistan," said the website, which offered a reward of up to $1 million for the 49-year-old Libyan.
Al-Libi purportedly was among al Qaeda leaders working in Libya since last year to establish a presence there.
In a video message to fellow Libyans distributed on jihadist forums in December, al-Libi said: "At this crossroads you have found yourselves, you either choose a secular regime that pleases the greedy crocodiles of the West and for them to use it as a means to fulfill their goals, or you take a strong position and establish the religion of Allah."
Al-Libi was captured in 2002 and imprisoned at Bagram Air Force Base in Afghanistan, according to the U.S. government, but he escaped in 2005.
In 2008, a statement posted on radical Islamic websites known to carry messages from al Qaeda described how four "military leaders" including al-Libi escaped from the prison, but the statement said then that one of the escapees -- Abu Abdallah al-Shami had been killed in a U.S. airstrike.
The statement said among those escaping with al-Shami was key al Qaeda figure Omar al-Faruq. Faruq died in a British airstrike after the escape.
Another escapee, Abu Nasir al-Qahtani, was captured in Afghanistan in 2006. With al-Shami's death, that left al-Libi as the only remaining member of that escape who had not been killed or captured.
U.S. President Barack Obama's administration recently justified its use of unmanned drones to target suspected terrorists overseas in a rare public statement, with John Brennan, the president's top counter-terrorism adviser, saying the strikes are conducted "in full accordance with the law."
The program utilizes unmanned aerial vehicles, often equipped with Hellfire missiles, to target suspected terrorist operatives in remote locations overseas -- with many such strikes occurring in Yemen and Pakistan, despite some internal opposition within the latter country.
Brennan said the United States "respects national sovereignty and international law" and is guided by the laws of war in ordering those attacks.
The area is widely believed to be the operating base for the Haqqani network and other militant groups that have attacked international troops in neighboring Afghanistan.
CNN's Barbara Starr contributed to this report
