Al Qaeda's No. 2 in Yemen died of wounds sustained in a U.S. drone attack last year in southern Yemen, the country's official news agency and a security official said Thursday.

Saeed al-Shihri, a Saudi national who fought in Afghanistan and spent six years in the U.S. military prison at Guantanamo Bay, was wounded in a missile attack in the southern city of Saada on Oct. 28, according to SABA news agency.

The agency said that he had fallen into a coma since then. It was not clear when he actually died.

A security official said that the missile had been fired by a U.S. -operated, unmanned drone aircraft. He spoke on condition of anonymity because he was not authorized to speak to the press.

Yemen had previously announced al-Shihri's death in a Sept. 10 drone attack in the province of Hadramawt. A subsequent DNA test however proved that the body recovered was not that of al-Shihri.

On Oct. 22, al-Shihri denied his own death in audio message posted on Jihadi websites.

Also known by the nom de guerre Abu Sufyan al-Azdi, he denounced at the time the Yemeni government for spreading the "rumor about my death ... as though the killing of the mujahideen (holy warriors) by America is a victory to Islam and Muslims."

Al-Shihri went through Saudi Arabia's famous "rehabilitation" institutes after he returned to his home country, but then he fled to Yemen and became deputy to Nasser al-Wahishi, the leader of an Al Qaeda group.

Al-Shihri's death is considered a major blow to Al Qaeda's Yemen branch, known as Al Qaeda in The Arabian Peninsula. Washington considers it the most dangerous of the group's offshoots.

Al Qaeda in Yemen has been linked to several attempted attacks on U.S. targets, including the foiled Christmas Day 2009 bombing of an airliner over Detroit and explosives-laden parcels intercepted aboard cargo flights last year.

In 2011, a high-profile U.S. drone strike killed U.S.-born Anwar al-Awlaki, who had been linked to the planning and execution of several attacks targeting U.S. and Western interests, including the attempt to down a Detroit-bound airliner in 2009 and the plot to bomb cargo planes in 2010.

Yemen, the Arab world's poorest nation, has fallen into lawlessness during a yearlong uprising starting in 2011, when millions of Yemenis took to the streets demanding the ouster of their longtime authoritarian ruler Ali Abdullah Saleh.

Al Qaeda militants exploited the unrest and took control of large swaths of land in the south until last spring, when the military, backed by the U.S., managed to drive hundreds of militants out of major cities and towns.

Since then, the group has carried out deadly attacks targeting mostly security and military officials, including suicide bombings that targeted military and security compounds.