At least four hostages held by the militants, including the U.S. journalist who was executed, were allegedly waterboarded early in their captivity.
Number of non-Afghan detainees in U.S. custody in Afghanistan has fallen below 30.
It is unclear whether Douglas McCain was fighting for the Islamic State, U.S. official says.
Qatar has privately become the go-to U.S. partner for indirect communications with Islamist groups.
The journalist had been held for almost two years by an al-Qaeda-affiliated group.
Doing so would put all Americans overseas at risk, State Department says.
Operation to rescue journalist James Foley, others earlier this summer drew heavy fire from militants.
Senior White House officials meeting on purported beheading of American journalist James Foley.
The militant group posted a video purporting to show the beheading of the American photographer.
Undercover FBI agent hosted Tunisian man in New York, but terrorism-related charges didn’t stick.