Al-Qaeda has announced the death of a top aide to Osama bin Laden, Mustafa Abu al-Yazid, a US monitoring group said Tuesday, in what would be a major blow to the global terror network. Yazid, an Egyptian national also known as Sheikh Said, was a founder member of Al-Qaeda and a former treasurer to bin Laden who became the network's Afghanistan chief three years ago. In Washington, a US official said there was strong reason to believe that Yazid -- widely regarded as Al-Qaeda's number three -- was dead and that he was killed recently in Pakistan's tribal areas. In terms of counterterrorism, this would be a big victory, the official said. Al-Masri was the group's chief operating officer, with a hand in everything from finances to operational planning, the official said, using another name for Yazid. He was also the organisation's prime conduit to bin Laden and Zawahiri, he said referring to Al-Qaeda number two and fellow Egyptian Ayman al-Zawahiri. He was key to Al-Qaeda's command and control.