Al-Shari was killed in Waziristan, according to a source cited by CNN. While there was no explanation how he was killed, it is known armed predator drones have been used to kill suspected terrorists.

"The loss of their chief of operations in Pakistan, an individual who played a key operational and administrative role for the group, will pose a challenge for (top Al Qaeda leaderAyman) al-Zawahiri," an unnamed official was quoted as saying.

"Abu Hafs was a contender to assume some of [recently killed Atiyah abd al-Rahman's] duties, coordinated Al Qaeda's anti-US plotting in the region, and worked closely with the Pakistani Taliban to carry out attacks inside Pakistan."

The strike will "further degrade" Al Qaeda's ability to recover from the Rahman killing in August because of his operations experience and connections within the group," a senior administration official said.

Earlier this week, the top Pentagon intelligence official said the pressure on Al Qaeda has left it in a "precarious" postiion and predicted that at this rate the group could be eliminated within the next two years.

"Its senior leaders are being eliminated at a rate far faster than Al Qaeda can replace them, and the leadership replacements the group is able to field are much less experienced and credible," said Michael Vickers, Under Secretary for Defense Intelligence Tuesday.

This year alone the terror group has lost eight of its "top 20" leaders and of all its top leaders from 2001 only one, Ayman al-Zawahiri, remains, he said. The killing of al-Shari raises the total to nine.