Pakistan has dismissed as "absurd" accusations that complicity or incompetence had allowed Al-Qaeda leader Osama bin Laden to hide out in the country for years and vowed a full investigation.
Addressing parliament in his first comments since bin Laden was killed by US special forces a week ago, Prime Minister Yousuf Raza Gilani said the official inquiry would be led by a top Pakistani general.
"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."
Pakistan is a key Washington ally in the US-led war on terrorism, but tense relations have been stretched even further by the discovery of bin Laden, dubbed OBL, living less than a mile from a military academy.
Gilani was also critical of Washington's operation to storm bin Laden's hideout in the leafy town of Abbottabad, about 55 kilometers (35 miles) from Islamabad without informing Pakistan first.
"Unilateralism runs the inherent risk of serious consequences," he warned amid growing domestic opposition to America's covert action on Pakistani soil.
But Washington emphatically refused Monday to say sorry for the raid which took out America's enemy Number 1, blamed for masterminding the September 11, 2001 attacks in which almost 3,000 people were killed.
White House spokesman Jay Carney said President Barack Obama was convinced he had done the right thing by sending in the special forces.
"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 reserves the right to act again against terror leaders in Pakistan if necessary.
Amid growing suspicion that there must have been some kind of collusion to enable the Al-Qaeda leader to live undetected in the town, Gilani said he had "full confidence in the high command of the Pakistan Armed Forces and the Inter-Services Intelligence (ISI)" spy agency.
Both have been accused of failing to spot bin Laden hiding under their noses or even perhaps further of even actively protecting him.
Obama on Sunday said the terror kingpin must have had some kind of backing.
"We think that there had to be some sort of support network for bin Laden inside of Pakistan," Obama told the CBS show "60 Minutes" on Sunday.
"But we don't know who or what that support network was."
And the head of the US Senate Intelligence Committee, Dianne Feinstein, charged Monday that bin Laden must have had help to evade capture and live as he did in Pakistan.
"I just don't believe it was done without some form of complicity," Feinstein said, delivering a stark and scathing warning to Islamabad and describing its ties with Washington as "increasingly problematic."
"I thoroughly agree with the administration's request that Pakistan take a good look at what the support services were for bin Laden," she added.
Helicopter-borne US Navy SEALs and elite forces carried out a raid lasting less than 40 minutes, killing bin Laden and seizing a vast haul of data from the compound in Abbottabad on May 2.
Senior US officials have said they had no proof that Islamabad knew about bin Laden's hideout.
But outraged US lawmakers have voiced suspicion that elements of Pakistan's military intelligence services must have known his whereabouts, and are demanding that billions of dollars in crucial US aid be suspended.
Similarly, Pakistanis are furiously asking whether their military was too incompetent to know bin Laden was there or, worse, conspired to protect him.
Gilani sought to deflect the criticism, blaming "all intelligence agencies of the world" for the failure to locate bin Laden in a decade-long manhunt, and declaring: "Pakistan is not the birthplace of Al-Qaeda."
"We did not invite Osama bin Laden to Pakistan or even to Afghanistan."
The highly influential military establishment is perceived to be Pakistan's strongest institution but the debacle has seriously embarrassed it.
It has hit back at criticism, demanding that the United States cut its troop presence in the country to a "minimum" and threatening to review cooperation if another unilateral raid is conducted.
Gilani also insisted Pakistan reserves the right to "retaliate with full force," although he stopped short of spelling what, if anything, would be done if the US staged another high-profile anti-terror raid.
But there were reports that the name of the top CIA agent in Islamabad had been allegedly divulged to a Pakistani newspaper.
Pakistani daily The Nation published the name Monday, and may have spelled it incorrectly, The New York Times reported, citing unnamed officials.
But a US official said: "There are currently no plans to pull the CIA's chief of station out of Pakistan" following the incident.
Obama meanwhile spoke Monday with Prime Minister Manmohan Singh of India to discuss the "successful American action" against bin Laden, the White House said.
White House National Security Advisor Tom Donilon has said the United States is now focusing its attention on bin Laden's longstanding deputy, the Egyptian Ayman al-Zawahiri.
Reportedly last seen in October 2001 in eastern Afghanistan, close to the lawless tribal regions along the Pakistan border, Zawahiri has released several videos from hiding, calling for war on the West.
The White House has meanwhile called on Islamabad to help counter growing mistrust by granting US investigators access to three of bin Laden's widows who are in Pakistani custody and could have vital information on Al-Qaeda.
Bin Laden's Yemeni wife, who was shot in the leg during the raid, has told investigators that the Al-Qaeda kingpin and his family had lived in the compound in Abbottabad for five years, an official said.