The Islamic State (IS) militant group is holding hostage a young American woman who was carrying out humanitarian aid work in Syria, it has emerged.
The 26-year-old woman is the third American known to have been kidnapped by the radical group.
The group recently threatened to kill American hostages to avenge the crushing air strikes in Iraq against militants.
The woman was captured last year while working with three humanitarian groups in Syria. Her family and US officials asked that she not be identified.
More than a week ago American freelance journalist James Foley was beheaded by IS, which kidnapped him in November 2012. Other American hostages have been held by militant groups, including Peter Curtis, who was recently released by al-Nusra Front, a rival Sunni extremist group.