A list of foreign hostages believed held by the Islamic State group and some of those who have been released, reportedly in exchange for ransom payments:
JOHN CANTLIE: The British photojournalist has appeared in several Islamic State propaganda videos delivering statements, purportedly from the Syrian border town of Kobani and Mosul, Iraq's second-largest city, likely under duress. Cantlie has worked for several British newspapers, including The Sunday Times, The Sun and The Sunday Telegraph, and was kidnapped with American journalist James Foley in November 2012. An Islamic State group militant beheaded Foley in August 2014.
FATHER PAOLO DALL'OGLIO: The Italian Jesuit priest went missing in July 2013 after traveling to meet Islamic militants in the Syrian city of Raqqa. He has not been seen since.
SAMIR KASSAB: A Lebanese national who worked as a cameraman for satellite channel Sky News Arabia. He was kidnapped Oct. 15 while working near Aleppo, Syria's commercial capital and the scene of heavy fighting since rebels seized part of the city in 2012.
ISHAK MOKHTAR: A Mauritanian reporter for Sky News Arabia. He was kidnapped Oct. 15 while working near Aleppo.
UNIDENTIFIED AMERICAN WOMAN: She was captured last year in Syria while working for aid groups. U.S. officials have asked that the woman not be identified out of fears for her safety.
THREE WORKERS FOR THE INTERNATIONAL COMMITTEE OF THE RED CROSS: They were taken near Saraqeb, in Syria's Idlib province, in October 2013. The organization has declined to provide information on their identities nor who has them, citing fears for their safety.
AROUND SEVEN LEBANESE SOLDIERS: Abducted in August during a cross-border militant raid in the Lebanese border town of Arsal.
The Islamic State group has released several hostages. None of the countries involved has provided any official confirmation that ransoms were paid to secure their release.
GRETA RAMELLI and VANESSA MARZULLO: The Italian aid workers, aged 20 and 21, returned home in January after being held hostage in Syria for more than five months.
NICOLAS HAMMARSTROM and MAGNUS FALKEHED: Swedish freelance journalists who were released in January after about 90 days in captivity. Swedish officials declined to say who seized them or how they were set free.
EDOUARD ELIAS, DIDIER FRANCOIS, NICOLAS HENIN and PIERRE TORRES: French journalists released in April after being held hostage for 10 months.
JAVIER ESPINOSA, RICARDO GARCIA VILANOVA and MARC MARGINEDAS: The Spanish journalists were released in March after being held hostage for months.