"All we can tell you is that by numbers and how the groups are operating in very remote locations and not collaboratively they're  fractured, ruptured, mitigated here.

"The question becomes, where would they go? What would they do?" he said.

Handwritten note

Anderson said: "United States Air Force F-16 aircraft attacked the target.

"Reporting indicated that several al-Qaeda members with ties to senior leadership were present at that time. Three were killed, including al-Tunisi," he said.

"His presence was confirmed by one of the two detainees from the  operation, one who left the target area just prior to the air strike, who we eventually captured minutes later," he said.

Ground forces recovered a handwritten note at the site that was believed to have been written by al-Tunisi, Anderson said, displaying a slide with photographs of the note.

"The key points in this hand-written note include, he's surrounded, communications have been cut and he's desperate for  help," he said.

"What I make of that is that we're having great success in isolating these pockets."

Anderson said al-Tunisi oversaw the movement of foreign fighters in Iraq and designated areas to them from where they could launch suicide attacks and car bombings in the Baghdad area.