American female aid worker Kayla Mueller, whose death was confirmed by the US on Tuesday, was not the last American hostage held in Syria, the White House has confirmed.
Till now, she was presumed to be the last American hostage held as a bargaining chip against the US government.
White House spokesman Josh Earnest admitted that there was at least one more captive, although he didn't confirm whether the person was held by the ISIS or some other militant group.
"There is at least one other hostage that is held in the region," he said in his daily briefing.
This comes as the US President Barack Obama confirmed on Tuesday the death of 26-year-old Mueller who was held by ISIS militants since August 2013. The cause of her death is unknown, although the militant group claimed last week that she was killed when a Jordanian airstrike hit a hideout where she was being held captive.
The deadly Sunni extremist group, also known as ISIL, has killed three other American hostages: journalists Steven Sotloff and James Foley, and aid worker Peter Kassig.
The White House spokesman said that he was unable to give more details about the other American hostage being held in Syria, because the US government didn't want to put the person's life in danger.
Although there is no official word, several Americans have gone missing in Syria since the civil war began in 2011, the most notable being Austin Tice, a freelance journalist reportedly captured in 2012. He was originally believed to have been held by the Bashar al-Assad government, reports New York Magazine.