Pakistan's Inter-Services Intelligence agency has been sheltering al-Qaeda chief Ayman al-Zawahiri in the port city of Karachi after he survived a drone strike in a remote area near the Afghan border last year, according to a media report.
Egyptian-born Zawahiri, a trained surgeon, has been protected by the ISI since US forces evicted al-Qaeda from Afghanistan in late 2001, Newsweek quoted several authoritative sources as saying.
His "most likely location", the sources said, is Karachi. "Like everything about his location, there's no positive proof," said Bruce Riedel, a 30-year CIA veteran who was the top adviser on South Asia and the Middle East for the past four US presidents.
"There are pretty good indications, including some of the material found in Abbottabad" (the Pakistani garrison town where Osama bin Laden was killed in 2011), "that point in that direction," Riedel said.
"This would be a logical place to hide out, where he would feel pretty comfortable that the Americans can't come and get him."
In the first week of January 2016, the Obama administration carried out a drone strike to target Zawahiri in the remote Shawal Valley in Pakistan's Federally Administered Tribal Areas, multiple sources told Newsweek.
An unnamed senior militant leader in the region said Zawahiri survived but five of his security guards were killed. "The drone
hit next to the room where Dr Zawahiri was staying," the militant leader said. "The shared wall collapsed, and debris from the explosion showered on him and broke his glasses, but luckily he was safe."
Zawahiri had "left the targeted room to sleep just 10 minutes ahead of the missile that hit that room", the militant leader said.
The militant leader further said Zawahiri had vowed that he would never be captured alive. He has a "desperate last wish" for one last big attack against America "before folding his eyes", the militant leader added.
Zawahiri had been in Pakistan's lawless semi-autonomous tribal region since 2005, according to the forthcoming book, The Exile: The Stunning Inside Story of Osama bin Laden and Al Qaeda in Flight, by British journalists Cathy Scott-Clark and Adrian Levy.
"Married to a local Pashtun girl, (Zawahiri) had been given a new home, a large mud-brick compound up in the hills" at Damadola, according to the book.
Riedel said Karachi was an ideal hideout for Zawahiri because it would be a "very hard" place for the US to conduct the kind of commando raid that killed bin Laden on May 2, 2011.
Unlike the sleepy garrison town of Abbottabad, the city of 26 million has a major nuclear complex and hosts naval and air bases, from where forces could quickly be scrambled to intercept foreign raiders.