A stunning new report showed how Pakistan's top spy agency may have secretly poisoned a CIA chief in the days and weeks after the U.S. raid that killed Usama Bin Laden in 2011.

The now-retired CIA station chief in Pakistan, Mark Kelton, had come down with a mysterious illness that left him in severe pain, The Washington Post reported Thursday. Current and former U.S. officials told the newspaper they suspected poisoning after attempts to treat him outside Pakistan failed.

Those officials said Pakistan’s Inter-Services Intelligence agency, or ISI, harbored grudges against diplomats, journalists and other people the country considered opponents. They said the head of the ISI, Ahmed Shuja Pasha, referred to Kelton as "the cadaver" instead of using his actual name.

Navy SEALs were credited with the raid on Bin Laden's Abbottabad compound that left the world's most wanted terror leader dead in May 2011. The United States' already-fragile relationship with Pakistan took a big hit in the following days when Pakistani police arrested a doctor who reportedly helped the CIA track down Bin Laden. Investigators said Dr. Shakeel Afridi set up a fake vaccination campaign to collect DNA samples from relatives of the terror boss.

Kelton reportedly left Pakistan after just seven months. He regained his strength after doctors performed abdominal surgery, according to the Post.

The retired CIA chief said he was not the first person to suspect he'd been poisoned, but added, "I’d rather let that whole sad episode lie." Nadeem Hotiana, a spokesman for the Pakistan Embassy, called the claims "fictional."

A CIA spokesman said the agency had uncovered no direct evidence of poisoning. But the U.S. previously accused the ISI of staging raids to cover up the deaths of some militants, and linked Pakistani intel to the 2008 terror attacks in Mumbai.

The newspaper reports it named Kelton because he'd posted parts of his CIA resume online.