The White House said on Wednesday that President Barack Obama reserved the right to take action again in Pakistan, as US outrage grew that Osama bin Laden was living in the allied nation.

Despite Islamabad's complaints that the raid that killed bin Laden was unauthorized and unilateral, Obama's spokesman Jay Carney said the President was prepared to target fugitives again if they are found in Pakistan.

"He made very clear during the campaign that that was his view. He was criticised for it," Carney told reporters.

"He maintained that that was his view and, by the actions he has taken as president, feels that it was the right approach and continues to feel that way."

During the 2008 presidential campaign, then-senator Obama said that he would order action against Bin Laden or other senior Al Qaeda leaders inside Pakistan if the country's leadership is "unable or unwilling to act."

Senator John McCain, the Republican candidate for president, accused Obama of effectively threatening a friendly nation and recommended that "you work with the Pakistani Government" if a target came into view.

Since taking office, Obama has ramped up the use of unmanned drones deep inside Pakistan, ordering more than 100 strikes in 2010 that killed over 670 people, despite protests by Islamabad that the attacks violate its sovereignty.

US officials said they gave no notice to Pakistan before on Sunday's daring raid, in which special forces killed the world's most wanted man at a mansion near the country's top military academy in Abbottabad.

CIA director Leon Panetta said the United States feared Pakistani officials may have otherwise alerted the Al Qaeda chief.

Pakistan has been on the defensive since on Sunday's attack, with civilian Prime Minister Yousuf Raza Gilani saying that the United States and other countries shared the blame for not finding Bin Laden sooner.

Washington has an uneasy partnership with Islamabad, which supported Afghanistan's hardline Taliban regime but switched sides overnight following the September 11, 2001 attacks by Al Qaeda.

Since then, the United States has provided some $18 billion in assistance to Pakistan. Most has gone to the military, but with Obama's support, Congress approved a five-year, $7.5 billion aid program in 2009 aimed at building schools, roads and democratic institutions.

Furious US lawmakers have called for a re-evaluation of relations after the Bin Laden case, charging that Pakistan is playing a double-game of supporting militants while enjoying a steady stream of money from the heavily indebted United States.

Representative Kay Granger, who chairs a key committee with oversight over foreign assistance, pressed the Obama administration to shelve nearly $200 million planned for survivors of Pakistan's major floods.

"My opposition to the program has only been heightened by the discovery of the most notorious terrorist in the world living hundreds of yards from a Pakistani military installation for more than five years," said Granger, a member of the rival Republican Party.

Granger said she could not defend the program to her constituents, charging the administration had denied federal disaster relief for her home state in the wake of wildfires that torched some 400 homes.

But the Obama administration is treading cautiously, with Carney saying Wednesday that more extremists have been killed in Pakistan than in any other country.

"The fight is not done, and we look forward to cooperating with Pakistan in the future," Carney said.

"The cooperation we've received from Pakistan has been very useful in that regard," he said.

Daniel Markey, a senior fellow at the council on Foreign relations, said the level of anger toward Pakistan in the US Congress was probably higher than ever before.

He warned that the United States had to "handle this current situation smartly," saying that the military — long the country's key institution — had lost face and may take it out against the United States.

Markey said that the United States had a vital interest in the development of Pakistan, a nuclear-armed country with a burgeoning population, grinding poverty and widespread anti-US sentiment.

"If left to current trends and trajectories, this will be a country by mid-century of over 300 million people, many of whom are poorly educated and incapable of being productive citizens within the global marketplace," he said.

"They will have few opportunities but to be disruptive unless things change."