Al-Qaeda’s branch in Yemen confirmed early Tuesday that a CIA drone strike killed its leader last week in a blow to the terror group as its militants appear to be benefiting from the widening unrest in the Arabian Peninsula country.

Nasir al-Wuhayshi, who pushed the group to engineer repeated terror plots against the United States, was targeted in the strike last week, according to U.S. officials who had said on Monday that it was too early to be certain he had been killed.

Wuhayshi’s death represents a substantial setback to an al-Qaeda affiliate that is regarded as the terrorist organization’s most dangerous franchise, with ties to several near-miss plots, including the attempted bombing of a Detroit-bound airliner in December 2009.

“Our Muslim nation, a hero of your heroes and a master of your masters departed steadfastly to God,” Khaled Batrafi, a senior al-Qaeda leader in Yemen, said in a video announcing the death.

Batrafi identified Wuhayshi’s deputy, Qassim al-Raimi, as the group’s new leader and pledged to continue fighting the “crusaders and their agents,” meaning the United States and its allies.

Nasir al-Wuhayshi, the leader of al-Qaeda in the Arabian Peninsula, in April 2012. In 2013, he was named al-Qaeda’s overall second-in-command. (AFP/Getty Images)

The affiliate, known as al-Qaeda in the Arabian Peninsula (AQAP), has exploited the chaos of assaults by Houthi rebels and an air war in Yemen by a Saudi Arabia-led coalition to expand control over territory in the southern Hadramout province. Analysts say that the newly acquired footholds could eventually be used by AQAP militants to stage attacks against the U.S. and Europe.

U.S. officials said Monday they were poring over intelligence related to a June 9 strike in Hadramout by the CIA that targeted Wuhayshi and other operatives of AQAP.

Wuhayshi’s demise could trigger a broader leadership crisis for al-Qaeda. As a former aide to Osama bin Laden, Wuhayshi fought to maintain the group’s focus on hitting Western targets, and in 2013 he was named al-Qaeda’s overall second-in-command and apparent heir to leader Ayman al-Zawahiri.

But even without Wuhayshi, AQAP is likely to remain a potent terrorist threat, according to U.S. officials and counterterrorism experts, who noted that the organization has regained considerable strength since the collapse of Yemen’s U.S.-backed government earlier this year.

Wuhayshi “is the designated successor and runs the most effective part of al-Qaeda,” said Bruce Riedel, a former CIA analyst who is a counterterrorism expert at the Brookings Institution.

Wuhayshi and Mokhtar Belmokhtar, an al-Qaeda veteran who may have been killed in a U.S. strike in Libya on Saturday, were among the few operatives with substantial ties to al-Qaeda’s founders, Riedel said. “But the ideology, the message and the mythology they created now outlives them, and I don’t think their passage is really going to be the end of this problem.”

The SITE Intelligence Group, which tracks postings by Islamist organizations on the Internet, said Monday that there was a flurry of postings by AQAP followers indicating that Wuhayshi had died and would be replaced by the group’s military commander, Qasim al-Rimi.

In one of his last public appearances, Wuhayshi took part in a brazen open-air gathering of al-Qaeda fighters in a remote stretch of Yemen last year. The group released a video in which Wuhayshi reiterated his emphasis on targeting the United States, saying, “We have to remove the cross, and the bearer of the cross, America.”

Wuhayshi was largely responsible for reestablishing a foothold for al-Qaeda in bin Laden’s ancestral home after the group was broken up inside Saudi Arabia in the years after the Sept. 11, 2001, attacks. He was among a group of militants who escaped a Yemeni prison in 2006 and three years later founded AQAP.

The Yemen franchise gradually eclipsed the terrorist network’s traditional core in Pakistan as a source of sophisticated plots. In addition to the attempt to bring down a Detroit-bound airliner with a bomb hidden in an operative’s underwear, AQAP used advanced explosives in plots to assassinate Saudi Arabia’s counterterrorism chief and hid bombs in printer cartridge packages meant to be shipped on international flights.

None of those bombs was detected by air travel screening systems. Instead, the plots failed only because the devices failed to detonate, missed their intended target or were discovered after a tip from a Saudi informant.

The group’s principal bombmaker, Ibrahim al-Asiri, also has been a target of U.S. airstrikes but is believed to have survived and shared his expertise with other recruits.

AQAP also claimed credit for the attack on the offices of the Charlie Hebdo satirical newspaper in Paris this year. U.S. officials have said that one of the brothers involved in the shooting had received training in Yemen.

After losing territory in recent years, AQAP has rebounded in recent months and forged new alliances with Sunni tribes in the Hadramout region of Yemen that feel threatened by the Houthis, Shiite rebels who seized control of the country’s capital early this year.

Although targeting the Houthis with airstrikes, the Saudi-led military coalition that launched its Yemen air war in March is not known to have attacked AQAP militants. Many Yemenis accuse the Saudis of effectively allying with the Sunni-extremist group against the Houthis, who are seen by officials in Riyadh as proxies of Shiite Iran.

Saudi Arabia, the region’s Sunni powerhouse, considers Iran its foremost nemesis.

The collapse of Yemen’s government forced the CIA and the Joint Special Operations Command to pull out counterterrorism teams that had worked closely with Yemeni security services in operations against AQAP in the country.

The strike aimed at Wuhayshi served as the latest reminder that the CIA and JSOC continue to operate armed drones over Yemen. But U.S. officials have said that much of the intelligence driving that air campaign came from joint U.S-Yemeni ground operations that were halted months ago.