SANAA, Yemen - The brother of Yemen's al Qaeda leader was among dozens of people killed in battles raging for days in the south of the country, security and military officials said Thursday.

A member of a local tribe confirmed that Abdel-Rahman al-Wahishi was killed in fighting Wednesday between Yemen's military and Islamic militants near the city of Zinjibar.

He was a younger brother of Nasser al-Wahishi, a Yemeni who once served as Osama bin Laden's personal aide in Afghanistan and now leads al Qaeda in the Arabian Peninsula. The younger al-Wahishi is believed to have been an operative in the group, but it is not clear what his role was in its hierarchy.

The security officials said faulty intelligence had indicated the military was firing on the al Qaeda leader himself, a high-value target for both the United States and Yemen's government. Further investigation revealed that the leader was not in the area at the time and that the man killed was the younger brother.

At least 51 people, including 18 soldiers, have been killed in the fighting since Sunday, according to an area hospital and the security officials, who spoke on condition of anonymity because they were not authorized to release the information.

Islamic militants, including some with links to the al Qaeda offshoot, seized control of Zinjibar and another town in April and May. They were taking advantage of the turmoil surrounding the popular uprising against President Ali Abdullah Saleh to expand their area of operations.

Al Qaeda in the Arabian Peninsula was behind several nearly successful attempts to attack U.S. targets, including the failed attempt to down a passenger jet bound for Detroit on Christmas Day 2009. Washington believes it is the most dangerous of several al Qaeda's offshoots around the globe.

President Saleh has cooperated with the U.S. in fighting the group and used the threat of al Qaeda in arguing that he could not relinquish power in Yemen despite the protests calling for him to go since February. The autocratic leader, however, signed a deal last month to transfer power in exchange for immunity from prosecution over the deaths of protesters and corruption during his 33 years in power.

Military units, including some who have defected to join the opposition to Saleh, have been battling the militants in Zinjibar off and on for months. The fighters, however, remain in partial control of the city, which is the provincial capital of Abyan province.

Thursday's fighting killed five militants and five soldiers. Residents reported heavy naval bombardment of the city, near Yemen's southern coast.

The security officials said the military commander of the al Qaeda in Yemen, Qassim al-Raimi, is believed to be in charge of the operation in Zinjibar.

Residents of Zinjibar have reported that many militants from different parts of Yemen, including the capital, Sanaa, have converged on the area to join the fighting.