Washington, May 3 (IANS) Asserting that it's "inconceivable" that Osama bin Laden did not have a support system in Pakistan, where he had been "hiding in plain sight" for years, the US is talking with Islamabad to determine what kind of benefactors the Al Qaeda leader had in that country.

"I think it's inconceivable that bin Laden did not have a support system in the country that allowed him to remain there for an extended period of time," White House counter terrorism adviser John Brennan told reporters Monday.

"I am not going to speculate about what type of support he might have had on an official basis inside of Pakistan," he said during a White House news conference.

Brennan said questions remain about how bin Laden could have stayed at the compound as long as he did. "People have been referring to this as 'hiding in plain sight,'" he said.

"Clearly, this was something that was considered as a possibility. Pakistan is a large country. We are looking right now at how he was able to hold out there for so long, and whether or not there was any type of support system within Pakistan that allowed him to stay there."

US officials are talking with the Pakistanis and will pursue all leads on what type of support system and benefactors that bin Laden might have had there.

Providing an insight into the decision process leading to the raid by US special operations forces that killed the Al Qaeda leader, Brennan called the attack a defining moment in the war against the terror group blamed for the Sep 11, 2001 attacks on the US.

The Defence Department and the CIA worked together to cut off "the head of the snake known as Al Qaeda," he said.

"It is going to have, I think, very important reverberations throughout the area, on the Al Qaeda network in that area," he said. "This is something that we've been after for 15 years. It goes back before 9/11."

Soon after taking office, President Barack Obama ordered the CIA and Defence Department to find and kill or capture bin Laden. Last year, intelligence indicated the terrorist was holed up in a million dollar compound in Abbottabad, a garrison town just 50 km north of Pakistani capital Islamabad.

Months of relentless examination strengthened that conclusion. And on April 29, the president made the decision to go after the Al Qaeda leader.