The former CIA chief in Pakistan believes Pakistani intelligence agents poisoned him after the American operation that killed Osama bin Laden in the terror master's Abbottabad compound.

Ex CIA Pakistan station chief Mark Kelton, who presided over the May 2011 raid on the compound, was rushed back to the states from Islamabad in "severe medical crisis," according to one official, with excruciating abdominal pains two months after bin Laden was killed by a Navy SEAL in the brazen night-time mission, reports the Washington Post.

Kelton's sudden illness was so severe and its cause so mysterious that officials suspected he had been poisoned by agents of Pakistan's Inter-Services Intelligence (ISI) agency, according to the Post. The official reasons given for Kelton's removal at the time were vague health concerns and deteriorating relations between the US and Pakistan.

Kelton has since retired from the CIA, and his health recovered following abdominal surgery. A link connecting his illness to ISI was never definitively proven.

Kelton, 59, declined requests for an interview from the Post, the newspaper reported, but he did say that the cause of his illness "was never clarified." He added that he was not the first to suspect that he had been poisoned. "The gen­esis for the thoughts about that didn't originate with me," he told the Post.

Of his tenure in Pakistan, he said: "I'd rather let that whole sad episode lie. I'm very, very proud of the people I worked with who did amazing things for their country at a very difficult time. When the true story is told, the country will be very proud of them." The poisoning suspicions were a sign of the increasingly fraught relationship between the two nations.

Already by 2009, US intelligence agencies reportedly had evidence that the ISI was complicit in the terrorist attacks in Mumbai, and were convinced that ISI agents tipped off terror targets before they could be struck by CIA drones. Pakistan's defence minister when bin Laden was killed has said the country's civilian and military leadership knew of the al-Qaeda chief's presence in the country.

By the time Kelton came on board in Islamabad in late 2010, tensions were high. The ISI chief at the time often refused to speak to Kelton or even utter his name, referring to the dour, acerbic CIA station chief as "the cadaver," according to officials.

Pakistani officials have denied the poisoning report. "Obviously, the story is fictional, not worthy of comment," said Pakistan Embassy spokesman Nadeem Hotiana. "We reject the insinuations implied in the allegations."