"But we don't know who or what that support network was. We don't know whether there might have been some people inside of government, people outside of government, and that's something that we have to investigate and, more importantly, the Pakistani government has to investigate."

The Pakistani government has promised a probe but has rejected charges that extremists like bin Laden are extended safe haven.

"They have indicated they have a profound interest in finding out what kinds of support networks bin Laden might have had," Mr Obama said.

"But these are questions that we're not going to be able to answer three or four days after the event. It's going to take some time for us to be able to exploit the intelligence that we were able to gather on site."

Since the pre-dawn raid a week ago that killed bin Laden, the number one enemy of the United States, outraged US lawmakers have called for billions of dollars in aid to Pakistan to be cut back or pulled entirely.

The Obama administration last year said it would seek another $US2 billion ($1.89 billion) for Pakistan's military, on top of a five-year, $US7.5 billion ($7.08 billion) civilian package approved in 2009 aimed at weakening the allure of Islamic extremists.

For a decade, Islamabad has been America's wary Afghan war ally, despite widespread public opposition and militant bomb attacks across the nuclear-armed country that have killed several thousand people.

Pakistan has never been fully trusted by either Kabul or Washington, which accuse its powerful military of fostering the Afghan Taliban it spawned during the 1980s resistance to the Soviet occupation of Afghanistan.

Pakistani intelligence officials deny the nation's Inter-Services Intelligence (ISI) agency had any idea bin Laden was holed-up in a compound in Abbottabad, which was raided in 2003 while still under construction.