Unknown assailants killed an officer of Yemen's Republican Guard forces in the southern port city of Aden on Friday night, security and medical sources said. Unidentified assailants driving a small pick-up truck shot Sanad Bader, a colonel of the elite Republican Guard troops, in Aden, a security source said. That was confirmed by a medical source who said that Bader's body, hit by a barrage of bullets, was sent to Naqeeb public hospital in Aden's neighborhood of Mansora. The masked assailants reportedly fled the scene and their whereabouts are unknown, according to the security source. No group has so far claimed responsibility for the drive-by shooting. But militants of the Yemen-based al-Qaida offshoot have been blamed for a series of assassinations, mostly in the country' s southern regions. The Yemen-based al-Qaida branch, known locally as Ansar al- Sharia, or Partisans of Islamic Law, emerged in January 2009. It's considered the most strategic threat to the Yemeni government and neighboring oil-rich Saudi Arabia. Earlier on Tuesday Yemen's armed forces launched an all-out offensive with more than 1,600 soldiers and 400 security personnel against several al-Qaida hideouts in the country's southern territories.