The CIA's Pakistani bureau chief was pulled out of the country just two months after the death of Osama Bin Laden with agonizing stomach pain, which may have been poison..

Mark Kelton, now 59, had previously worked in Moscow when he was brought in to oversee the CIA's Pakistani bureau, which had a fraught relationship with the country's Inter-Services Intelligence Department (ISI).

That relationship got dramatically worse very quickly - and saw Kelton flying out of the country seven months later in agony, taken down by what some in the agency suspect was a poisoning, The Washington Post reported.

Boss: Mark Kelton (pictured) was head of the CIA's Pakistan bureau in 2011, but had to quit after suffering agonizing stomach pains that some believe were caused by a rival intelligence agency poisoning him

A poisoning was never confirmed and both sides have officially denied the claim.

However, sources said the CIA took the possibility seriously, that a poisoning could well have happened, and that some still believe it did.

Top target: Kelton oversaw the raid in which Osama bin Laden was killed - leading to claims that Pakistani officials were hiding the terrorist. In retaliation, Kelton's name was leaked to press

The CIA even searched for evidence that Kelton - whose role at the CIA had been revealed by Pakistani press just before he fell ill, and whose relationship with the ISI chief had completely collapsed - was targeted.

If he was, it would come as little surprise, given how much his success at the Pakistan bureau were matched by the ISI's hatred for him.

Kelton's previous role in Moscow had seen him skirmishing with the KGB and its successor during and after the Cold War, and he brought that mentality to Pakistan, telling staff to stop treating the ISI like a belligerent partner and start treating them like an enemy.

If the ISI was keeping a list of black marks against Kelton's name, this would have been the first.

The second would come just 48 hours after he landed, when CIA contractor Raymond Davis was arrested on January 27 after shooting and killing two Pakistani men that he said tried to rob him.

Kelton told Cameron Munter, then the US Ambassador, not to admit Davis was a CIA contractor - despite his car being found to be full of spy gear, including a disguise kit.

Munter said that would patronize Pakistani officials, but even President Obama referred to Davis as a 'diplomat' for over a month until Munter was able to deal directly with then-ISI chief Ahmed Shuja Pasha.

After a secret trial Davis, a worker for the Blackwater private security firm, was released on March 16 - in exchange for a payment of $2.4million to the families of the men he'd killed.

His release coincided with the return of US drone bombings, which had largely stopped while Davis was imprisoned, and which are hated by members of the Army and ISI, who see them as the US overstepping their bounds.

ISI agents have even whipped up anti-American sentiment after drone bombs killed innocent civilians, The New Yorker has reported.

Pasha was furious about the drones coming back, The Washington Post said, and called the renewed bombings 'a kick in the teeth'. He reportedly refused to deal directly with Kelton ever again.

Troubles: Kelton's troubles began months earlier, when CIA contractor Raymond Davis (right, with his lawyer) killed two Pakistani men. Kelton refused to admit Davis's CIA connection, upsetting Pakistani authorities

Drones: And things got worse after the US negotiated Davis's freedom. The next day drone strikes, which had stopped briefly, began again. Kelton's Pakistani counterpart, who hated strikes, called it 'a kick in the teeth'

In May 2011, the Pakistani bureau achieved one of its greatest victories when Osama bin Laden's compound in the city of Abbottabad.

But this success only damaged the US-Pakistani relationship further, as some called the ISI incompetent and others - including then-CIA Director Leon Panetta - suggested Pakistani officials had actively hidden the terrorist kingpin.

In retaliation, senior officials leaked information about the CIA's operations to Pakistani press.

Counterpart: Kelton's counterpart at the time was Ahmed Shuja Pasha (pictured), chief of the Inter-Services Intelligence Department. He loathed Kelton and refused to speak to him

That information included not just the existence of a CIA safe house in Abbottabad or the agency using a Pakistani doctor to get DNA samples from bin Laden's compound, but also Mark Kelton's name and rank.

The chief's surname was misspelled as 'Carlton' but it was danger enough.

Soon after, Kelton began to experience severe stomach pains. At first it seemed as though he might just be responding poorly to local food - something common among Westerners living in Pakistan.

But the pains got worse. Kelton began to miss days of work, and flew out of the country to receive treatment that proved utterly useless.

So the agency began to suspect he might be being poisoned.

Current and former US officials told The Washington Post that the ISI has been linked with 'numerous plots' against journalists and diplomats - as well as other perceived threats to themselves or the state.

And while a full investigation never took place, the CIA did look through its intelligence to see if Kelton - who left the Pakistan post in July 2011 and then underwent abdominal surgery - could have been poisoned.

The CIA confirmed that it never found any proof, and Pakistan Embassy spokesman Nadeem Hotiana told the Post, 'Obviously the story is fictional, not worthy of comment.'

But in a brief phone interview with the Post, Kelton - who had declined to explain the details of his abdominal operation - confirmed that the agency did take the possibility of an attack on his life seriously, and even suggested the possibility in the first place.

'The gen­esis for the thoughts about [being poisoned] didn’t originate with me,' he said.