Al-Qaeda announced its new leader on Thursday, elevating Ayman al-Zawahiri, an Egyptian who had been operational commander of the global terror network and served as its public face in recent years.

Zawahiri, a surgeon who spent years in underground Islamic groups in Egypt before joining al-Qaeda, previously was the militant group’s second-in-command. Since the death of Osama bin Laden in a U.S. raid last month, he had been considered the most likely candidate to take the helm of the organization.

Zawahiri, 59, is regarded as a deeply religious leader who had the skill and experience to help turn an Afghan guerrilla movement into a global terrorist organization. But he is also considered rigid and lacking in charisma, and terrorism experts say it is unclear whether he can rebuild an organization that has been under siege by U.S. military and intelligence forces.

U.S officials and terrorism analysts had speculated that Zawahiri might face competition for the job of al-Qaeda leader from other candidates, such as Libyan jihadists Atiyah Abd al-Rahman and Abu Yahya al-Libi, both of whom were considered more personable.

But al-Qaeda’s general command put out a statement on Thursday announcing Zawahiri’s appointment, according to the SITE Intelligence Group, which monitors developments in radical Islamic groups.

“As the best form of gratitude for the righteous martyr and for the life of the mujahid Sheikh Osama bin Laden is to continue on the path of jihad . . . the General Command of Qaeda . . . announces that Sheikh Dr. Abu Muhammad Ayman al-Zawahiri . . . has assumed the responsibility of the leadership the group,” the statement said, according to SITE.

The statement, published on various jihadist Web sites, said the al-Qaeda would continue to urge Muslims to fight “against the disbelieving invaders who attack the lands of Islam, headed by Crusader America, and its maid, Israel, and those who help them.”

Rita Katz, director of SITE Intelligence Group, called Zawahiri “the most logical successor for bin Laden.”

“As one of al-Qaeda’s earliest leaders and ideologues who deeply understands how the organization operates, he continues to enjoy great respect within the global jihadist community and is currently al-Qaeda’s most prominent figurehead,” Katz said in an e-mail.

U.S. forces have launched dozens of strikes this year on suspected al-Qaeda hideouts near Pakistan’s border with Afghanistan. As a result, analysts, say al-Qaeda’s central leadership appears to have been severely weakened. Its Yemeni branch has emerged as a more powerful and active group.

Two of al-Qaeda’s senior operatives were killed in the past few weeks: Ilyas Kashmiri, who was implicated in the 2008 Mumbai attacks, and Fazul Abdullah Mohammed, believed to have planned the 1998 U.S. Embassy bombings in East Africa.

Since the Sept. 11, 2001, terror attacks, Zawahiri has been al-Qaeda’s most visible spokesman, releasing dozens of audio and video statements, as bin Laden lay low. He is in hiding, however, with his whereabouts unknown.

Zawahiri, from a prominent Egyptian family, plunged into radical politics as a teenager and later went on to lead Egyptian Islamic Jihad.

He and hundreds of other Islamists were jailed after the assassination of President Anwar Sadat in 1981. He later said he was tortured in prison, which steeled his desire to overthrow Egypt’s pro-Western, military-backed government.

After his release, he went into exile and eventually went to Pakistan to assist the mujaheddin fighting in Afghanistan. Zawahiri merged his group with bin Laden’s in 2001, months before the al-Qaeda attacks on New York and Washington.

Zawahiri promoted the use of suicide bombings and is believed to have helped plot the 2000 bombing of the USS Cole in Yemen.

In a videotaped eulogy to bin Laden released June 8, Zawahiri said the slain leader will remain a “source of horror and a nightmare chasing America, Israel and their allies.”