Editor's Note: This story has been updated since it was first published. The original version of this story said that a Pakistani asset told the U.S. where bin Laden was hiding. Sources say that while the asset provided information vital to the hunt for bin Laden, he was not the source of his whereabouts.

Intelligence sources tell NBC News that in the year before the U.S. raid that killed Osama bin Laden, a retired Pakistani military intelligence officer helped the CIA track him down.

While the Pakistani intelligence asset provided vital information in the hunt for bin Laden, he did not provide the location of the al Qaeda leader's Abottabad, Pakistan compound, sources said.

Three sources also said that some officials in the Pakistani government knew where bin Laden was hiding all along.

The asset was evacuated from Pakistan and paid reward money by the CIA, sources said. U.S. officials took pains to note he was one of many sources who provided help along the way, and said that the al Qaeda courier who unwittingly led them to bin Laden, Ahmed al-Kuwaiti, remained the linchpin of the operation.

The U.S. government has always characterized the heroic raid by Seal Team Six that killed bin Laden as a unilateral U.S. operation, and has maintained that the CIA found him by tracking the courier.

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The new revelations do not cast doubt on the overall narrative that the White House began circulating within hours of the May 2011 operation. The official story about how bin Laden was found was constructed in a way that protected the identity and existence of the asset, who also knew who inside the Pakistani government was aware of the Pakistani intelligence agency's operation to hide bin Laden, according to a special operations officer with prior knowledge of the bin Laden mission.

While NBC News has long been pursuing leads about a "walk in" intelligence asset and about what Pakistani intelligence knew, both assertions were made public in a London Review of Books article by investigative reporter Seymour Hersh. Hersh's story, published over the weekend, raises numerous questions about the White House account of the SEAL operation. It has been strongly disputed both on and off the record by the Obama administration and current and former national security officials.

The Hersh story says that a "walk in" asset, a former Pakistani military intelligence official, contacted U.S. authorities in 2010 and told them bin Laden was hiding in Abbottabad; that elements of ISI, the Pakistani intelligence agency, knew of bin Laden's whereabouts; and that the U.S. told the Pakistanis about the bin Laden raid before it launched. The U.S. has maintained that it did not tell the Pakistani government about the raid before it launched.

On Monday, Pentagon spokesman Col. Steve Warren called Hersh's piece "largely a fabrication" and said there were "too many inaccuracies" to detail each one. Col Warren said the raid to kill bin Laden was a "unilateral action." Both the National Security Council and the Pentagon denied that Pakistan had played any role in the raid.

Pakistani media personnel and local residents gather outside the hideout of al Qaeda leader Osama bin Laden in Abbottabad, Pakistan after the U.S. raid that killed him. AAMIR QURESHI / AFP/Getty Images

"The notion that the operation that killed Osama Bin Laden was anything but a unilateral U.S. mission is patently false," said NSC spokesman Ned Price. "As we said at the time, knowledge of this operation was confined to a very small circle of senior U.S. officials."

Sen. John McCain, chairman of the Senate Armed Services Committee, dismissed Hersh's account. "I simply have never heard of anything like this and I've been briefed several times," said McCain, R.-Arizona. "This was a great success on the part of the administration and something that we all admire the president's decision to do. "

The NBC News sources who confirm that a former Pakistani military intelligence official became a U.S. intelligence asset include a special operations officer and a CIA officer who had served in Pakistan. These two sources and a third source, a very senior former U.S. intelligence official, also say that elements of the ISI were aware of bin Laden's presence in Abbottabad. The former official was emphatic about the ISI's awareness, saying twice, "They knew."

Another top official acknowledged to NBC News that the U.S. government had long harbored "deep suspicions" that ISI and al Qaeda were "cooperating." And a book by former acting CIA director Mike Morrell that will be published tomorrow says that U.S. officials could not dismiss the possibility of such cooperation.

None of the sources characterized how high up in ISI the knowledge might have gone. Said one former senior official, "We were suspicious that someone inside ISI … knew where bin Laden was, but we did not have intelligence about specific individuals having specific knowledge."

Multiple U.S. officials, however, denied or cast doubt on the assertion that the U.S. told the Pakistanis about the bin Laden raid ahead of time.