Washington, May 9 (IANS) After killing Al Qaeda leader Osama biLaden, the United States is now hunting for his deputy Ayman al Zawahiri, but it still may not tell Pakistan if he is targeted.

It would depend on "the specifics of the operation," White House National Security Advisor Tom Donilon told ABC Sunday when asked whether the US would inform Pakistan if it decided to target al Zawahri

"This really wasn't a matter of trusting or not trusting; it was a matter of operational security," he said, referring to the secrecy surrounding the May 1 raid on bin Laden's Abbottabad hideout and the decision not to inform the Pakistani government.

Donilon also told CNN that al Zawahiri the Egyptian surgeon who is likely to emerge as the new chief of the terror outfit, would be the next most wanted terrorist on it list.

"Al Zawahiri will be the next number one terrorist that we're looking for in the world. But we have a broad and global effort," he said.

Describing the killing of bin Laden as "the most significant achievement against Al Qaeda and our nation's efforts against Al Qaeda over the last ten years," Donilon said the "amount of intelligence we got as a result of the raid, in addition to taking out bin Laden, is really extraordinary."

When the US commandos raided bin Laden's hideout they "were fired upon. They had to breach several walls and doors to get to where Osama bin Laden was.

"At no point during the course of this operation did Osama bin Laden indicate that he was prepared to surrender," he said in justification of killing an unarmed bin Laden.

From a strategic point of view, the message of the raid "was of United States carrying out here over the course of two administrations, a persistent, deliberate and dedicated effort to achieve its goals."

The message is that the United States will carry out and execute now what it says it's going to do, and it has the capability to do so," Donilon said.