Iraq and Syria: The hostages
Four Western hostages have been beheaded by Islamic State militants.
They were among dozens of journalists and aid workers being held hostage in Iraq and Syria.
Some are believed to be being held by IS and other militant groups, while others may be in the custody of Syrian regime forces.
Here are some of those whose details have been made public.
Austin Tice, 34, is an American journalist who has reported for the McClatchy group.
His family say he was taken captive near the Syrian capital Damascus on 14 August 2012.
Mr Tice, who had served in the US Marine Corps, entered Syria in May that year.
Friends say he quickly fell in love with Syrian culture and food.
He was born and raised in Texas, and won the 2012 George Polk Award for War Reporting.
No group has yet taken responsibility for his capture, and his whereabouts are not yet known.
Ishak Moctar is a reporter for Sky News Arabia and a Mauritanian national.
He was captured along with his colleague Samir Kassab and Syrian driver in October 2013.
The driver was later released but nothing has been heard from Mr Moctar or Mr Kassab since.
Abu Dhabi-based Sky Arabia has appealed for information that would lead to their safe return.
No group has yet claimed responsibility for their capture.
Samir Kassab, a 29-year old Lebanese national, is a cameraman for Sky News Arabia.
He was abducted along with his colleague Ishak Moctar in October 2013 while they were working near Aleppo, Syria.
His family had tried to dissuade him from working in the country, asking him: "Is there nothing else except Syria?"
Three ICRC workers
Three workers from the International Committee of the Red Cross remain unaccounted for after they were captured in northern Syria on 13 October 2013.
Four of their colleagues were also taken in the attack on their convoy but freed the next day.
The convoy was intercepted by unidentified armed gunmen near the town of Saraqeb in Idlib province.
The nationalities of those captured have not been released, and it is not yet known who carried out the attack.
The Guardian reported on 20 August that four more foreigners had been taken hostage near Aleppo.
They included two Italian women, a Dane and a Japanese national, the paper said.