Image copyright Getty Images

The charges are explosive - and cut against a heroic narrative that defined, in part, arguably the greatest foreign policy success of President Barack Obama's first term in office.

According to Pulitzer Prize-winning author Seymour Hersh, the US raid that killed al-Qaeda leader Osama Bin Laden was not a secret, risky US action, it was a joint operation between the US and Pakistani military intelligence.

The allegation has many in the US - and Pakistan - crying foul, and pointing to what they see as insufficient attribution and questionable conclusions throughout Hersh's lengthy piece.

"The notion that the operation that killed Osama Bin Laden was anything but a unilateral US mission is patently false," said White House spokesperson Ned Price, adding that the piece was riddled with "inaccuracies and baseless assertions".

At the heart of Hersh's article is the allegation that, starting in 2006, Bin Laden was under Pakistani control, kept in Abbottabad with the financial assistance of Saudi Arabia.

Hersh says high-level Pakistani officials consented to allow the US to conduct its "raid" on the compound - a de facto assassination - after the US found out about Bin Laden's whereabouts through a source in Pakistani intelligence (and not, as reported, after interrogation of al-Qaeda detainees and extensive investigation into a Bin Laden courier).

A deal was then struck that included allowing the US to set up detailed surveillance of the area, obtaining DNA evidence confirming Bin Laden's identity and even providing a Pakistani agent to help guide the operation - in exchange for continued US financial support of the nation's intelligence service and its leaders.

Image copyright Getty Images Image caption Hersh says Mr Obama was supposed to wait a week to announce Bin Laden's death

As part of the agreement, according to Hersh, the US would hold off on announcing Bin Laden's death for a week, and then only say that he was killed in a drone strike in Afghanistan. Mr Obama double-crossed the Pakistanis, however, after one of the US helicopters crashed during the operation and the White House feared they could not contain the story.

Instead Mr Obama spoke to the nation that night, announcing that US Navy special forces had conducted a daring attack based on months of secret intelligence-gathering, without the knowledge of the Pakistanis, concluding in a firefight in which Bin Laden - and other militants - were killed.

In the following days, further details - sometimes conflicting and later disavowed - leaked out from the White House, angering US special forces commanders and defence officials.

Image copyright Getty Images Image caption Seymour Hersh says he "understands the consequences" of his article

"The White House's story might have been written by Lewis Carroll," Hersh writes in the latest issue of the London Review of Books, referencing the author of Alice in Wonderland.

His piece ends with a broad-based condemnation of the Obama administration's foreign policy operation.

"High-level lying nevertheless remains the modus operandi of US policy, along with secret prisons, drone attacks, Special Forces night raids, bypassing the chain of command and cutting out those who might say no," he writes.

Word of Hersh's story spread quickly, dominating political conversation on social media and repeatedly crashing the London Review of Books' website due to the heavy volume of traffic.

It also didn't take long before some of Hersh's fellow journalists began questioning the story, most notably Max Fisher of Vox and Peter Bergen of CNN. The critiques fall into a few major categories:

• Unreliable sources. Much of Hersh's article is based on the claims of unnamed intelligence officials in the US and Pakistan, none of whom were directly involved in the operation. The only named source, Asad Durrani, served in the Pakistani military intelligence more than two decades ago and says only that "former colleagues" of his back up Hersh's claims. Durrani was later contacted by CNN's Bergen, and he would only say that Hersh's account was "plausible".

• Contradictory claims. Hersh disregards the fact that two of the Navy Seals involved in the attack on Bin Laden's compound have come out with details of the raid that directly contradict his account. Bergen, who visited the compound after the operation, writes that there was clear evidence of a protracted firefight, as the location was "littered almost everywhere with broken glass and several areas of it were sprayed with bullet holes".

• Unrealistic conclusions. Why would the Saudis support a man who wanted to overthrow the Saudi monarchy? Why, if US support for Pakistan was part of the bargain, did US-Pakistani relations deteriorate in the years after the raid? If the US and Pakistan were co-operating, was a staged raid really the simplest possible way to ensure that Bin Laden was killed?

As is often the case with conspiracy theories, perhaps the sharpest criticism of Mr Hersh's narrative is that it relies on a large cast of characters operating effectively while maintaining universal secrecy. Vox's Fisher accuses Hersh - who won a Pulitzer in 1970 for exposing the My Lai massacre of Vietnamese civilians at the hands of US soldiers - of producing a growing number of difficult-to-believe exposes based on tenuous evidence.

Image copyright Getty Images Image caption Hersh says Bin Laden's compound was under the control of Pakistani military intelligence

In the last three years, for example, he has penned pieces alleging the George W Bush administration trained Iranian militants in Nevada and that Turkey was behind chemical weapons attacks in Syria.

"Maybe there really is a vast shadow world of complex and diabolical conspiracies, executed brilliantly by international networks of government masterminds," Fisher writes. "And maybe Hersh and his handful of anonymous former senior officials really are alone in glimpsing this world and its terrifying secrets. Or maybe there's a simpler explanation."

Meanwhile, conservative commentators in the US, who have long chafed at some of Hersh's accusations about US actions during the Bush administration, celebrated the criticism - while noting what they saw as the key motivating factor.

Image copyright Getty Images Image caption Americans celebrated when they heard Bin Laden was dead

"When Seymour Hersh manufactures crazy against Obama, suddenly he's a crank, not an elder statesman," tweets Breitbart's John Nolte. "With Bush he was a media GOD."

In a television interview on Monday, Hersh tried to turn the tables, saying that the US account of the operation is the one that's unbelievable.

"Twenty-four or 25 guys go in to the middle of Pakistan, take out a guy with no air cover, no protection, no security, with no trouble - are you kidding me?" he said.

"Look, I'm sorry it goes against the grain," he added. "I've been doing this my entire life, and all I can tell you is I understand the consequences."

There's a bit of internet shorthand, frequently used on Twitter, to preface an allegation that seems explosive but questionable: "Whoa if true".

It seems the reaction to Hersh's piece so far has included a lot of "whoa" - but with a heavy emphasis on the caveat, "if true".