Washington: A US lawmaker, who heads the key Congressional intelligence committee, said on Tuesday that at least half a dozen top Al Qaeda leaders are taking shelter in Pakistan.

"Of the 20 senior leaders in al-Qaeda, at least a dozen of them, we believe to be travelling around Pakistan," Congressman Mike Rogers, chairman of the powerful House Permanent Select Committee on Intelligence, told reporters at a news conference.

Rogers said US lawmakers would be seeking answers from Pakistan that how Osama bin Laden lived so close to Islamabad.

He was killed on Sunday in an operation by the US Special forces in garrison town of Abbottabad.

"I don't want to speculate if they did or they did not. I mean, we're going to ask those questions. I think Americans have the right to know that. I would like to know that they knew," Rogers said.

"But at the same time, we have to remember there are still equities that we have in Pakistan as it relates to our national security. We know there are some incredibly bad people there," he noted, adding, it is important for the US that it maintains a relationship Pakistan.

"Keeping a diplomat for 42 days, all of those things -- there's been some speculation in the past about release of information to bad guys through their ISI. All of those things remain a tension for the United States and Pakistan. We hope that we can work our way through it. Doesn't mean that we're not going to ask hard questions," Rogers said.

The powerful Republican Congressman said the information started on it four years ago under George Bush administration.

"I don't draw the nexus between going into Afghanistan and Iraq and not being able to get bin Laden. The reason we had such difficulty is because of his operational security, the way he conducted himself and operated," he said.

"I mean, think about this, the million-dollar compound plus, which is outlandish by that region of Pakistan that was built to repel any operation just as it happened. No Internet connectivity. They would use cut-outs to cut-outs, meaning they had people who met people they didn't know to deliver a message to another person they didn't know, who eventually worked its way back to Osama bin Laden," he said.

The Congressman said to track bin Laden was "very tricky business".

"And we don't get to walk around every place we want in the world knocking on doors doing an FBI-style investigation about where is somebody," Rogers said.

Rogers, who has access to classified intelligence information, said it is unlikely that the retaliation from al Qaeda would happen so soon.