Deputy leader of al Qaeda in the Arab Peninsula, Said al-Shehri, a Saudi national identified as Guantanamo prisoner number 372, speaks in a video posted on Islamist websites, in this 2009 file image.
Yemeni armed forces have killed Said al-Shehri, a man seen as the second-in-command of al-Qaida in the Arabian Peninsula (AQAP), a government website said on Monday.
The Ministry of Defense website said Shehri was a Saudi national who was killed, along with six other militants, in an army operation in the Wadi valley in south-east Yemen. It gave no more details.
The United States has used unmanned drones to target AQAP, which has planned attacks on international targets including airliners and is described by Washington as the most dangerous wing of al-Qaida.
A Yemeni security source said Shehri was killed in an operation last Wednesday which was thought to have been carried out by a U.S. drone, rather than the Yemeni military. The source said another Saudi and an Iraqi national were among the others killed.
Shehri is a former inmate of the U.S. detention facility at Guantanamo Bay who was released to Saudi Arabia in 2007 and put through a Saudi rehabilitation program for militants.
Yemen's government is trying to re-establish order after an uprising pushed out veteran ruler Ali Abdullah Saleh in February, but faces threats from Islamist militants, southern secessionists and a Shiite rebel movement in the north.
The protests and factional fighting have allowed al-Qaida's regional wing to seize swathes of south Yemen, and Shiite Muslim Houthi rebels to carve out their own domain in the north.
The lawlessness has alarmed the U.S. and Yemen's much bigger neighbor Saudi Arabia, the top world oil exporter, which view the impoverished state as a new front line in their war on al-Qaida and its affiliates.
Washington, which has pursued a campaign of assassination by drone and missile against suspected al-Qaida members
, backed a military offensive in May to recapture areas of Abyan province.
But militants have struck back with a series of bombings and assassinations.
Reuters and NBC's Mohammed Muslemany in Cairo contributed to this report