The United States refused to say sorry on Monday for taking out Osama bin Laden in Pakistan, after its estranged anti-terror ally warned it would retaliate against any future strikes.
Amid a deepening crisis between the two uneasy partners, Washington pressed for access to three of the dead al Qaeda chief's widows, who it believes may have valuable information on bin Laden's movements and on the terror group.
In a further sign of tension over last week's daring covert raid in Abbottabad, the New York Times meanwhile reported that Pakistani authorities had retaliated by leaking the name of the CIA chief in Islamabad to the media.
Pakistani Prime Minister Yousuf Raza Gilani, under intense domestic pressure over his country's failure to detect the stealth US special forces raid, earlier hit out at American unilateralism and warned against future US action.
He also insisted Pakistan reserves the right to "retaliate with full force," although he stopped short of spelling out what, if anything, would be done if US President Barack Obama ordered another unilateral anti-terror raid.
But at the White House, spokesman Jay Carney said Obama was convinced he had done the right thing by sending in special forces at the dead of night in a raid in which bin Laden was killed in his Pakistani lair.
"We obviously take the statements and concerns of the Pakistani government seriously, but we also do not apologize for the action that we took, that this president took," Carney said.
"It's simply beyond a doubt in his mind that he had the right and the imperative to do this," said Carney, who has warned that Obama reserved the right to act again against terror leaders in Pakistan if necessary.
But with the US relationship with Pakistan -- which has enjoyed hundreds of millions of dollars of US aid -- slumping deeper into crisis, Carney stressed that ties with Islamabad were "very important" to Washington.
"Our need for cooperation remains very important," Carney said, adding that Washington was conducting a full probe, using intelligence seized from bin Laden's compound to assess the al Qaeda's networks support system in Pakistan.
Carney repeated the point made by his superiors that there was so far no reason to suspect that senior Pakistani government officials knew bin Laden was hiding in the garrison city close to Islamabad, possibly for years.
At the State Department, spokesman Mark Toner said cooperation between Pakistan and Washington had yielded "tangible results" over a decade, but admitted the two sides did not always see "eye-to-eye."
The Times report that for the second time in five months, the authorities in Pakistan had leaked the name of the CIA station chief in Islamabad, hinted at a souring of ties between US spies and Pakistan's Inter-Services Intelligence Directorate (ISI).
But a US official said the Central Intelligence Agency had no plans to withdraw its top spy from Islamabad after his name was allegedly divulged in a Pakistani newspaper.
Many US analysts suspect the ISI of at the very least backing elements of the Taliban and al Qaeda, and some believe that ISI officers at some level must have known of bin Laden's whereabouts and may even have shielded him.
On Sunday, Obama told the CBS Show "60 Minutes" that Pakistan must investigate how bin Laden, on the run since al Qaeda masterminded the September 11 attacks in 2001, had remained undetected for so long.
"We think that there had to be some sort of support network for bin Laden inside of Pakistan," Obama said.
"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."
Gilani however hit back on Monday, saying accusations that bin Laden must have benefited from official complicity or incompetence to hide in Pakistan were "absurd."
"We are determined to get to the bottom of how, when and why about OBL's presence in Abbottabad," he said. "Allegations of complicity or incompetence are absurd. We emphatically reject such accusations."
Toner commented that Washington was waiting for answers, but did not expect them to come "quickly."