The Yemen-based al-Qaida offshoot claimed responsibility in an online statement on Thursday for a terrorist attack on an army headquarters in Yemen's southern port city of Aden, killing at least 16 people and injuring several others.

Scores of masked attackers stormed on Wednesday the Fourth Military headquarters in the coastal district of Tawahi in Aden through the rear door, spreading bullets and rocket propelled grenades at the main gate during the morning service.

The al-Qaida in the Arabian Peninsula (AQAP) based in Yemen posted a statement on Islamic websites, claiming it conducted Wednesday's assault to "strike at the U.S. drone program and the joint operation rooms that targets AQAP leaders and operatives."

AQAP said that up to "50 army soldiers and officers" were killed during the well-planned attack against the army headquarters.

The statement warned the military authorities not to cooperate with Americans in the war against al-Qaida, saying the attack was "only a message which will be followed by others."

About six al-Qaida members, five soldiers and five civilians were killed in the fierce clashes that followed the attack, including women and children, medical and police sources told Xinhua.

Last month, al-Qaida militants killed 24 Yemeni soldiers of the Special Forces in an attack on a military barracks in the southeast province of Hadramout.

Militants of the Yemen-based al-Qaida offshoot were blamed by the country's government for a series of assassinations and armed attacks, mostly in the country's southern regions.

AQAP, which emerged in January 2009, is considered the most strategic threat to the Yemeni government and neighboring oil-rich Saudi Arabia. Endi