Here is look at 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: British photojournalist who appeared in several Islamic State propaganda videos delivering statements, purportedly from the Syrian border town of Kobani and the Iraqi city of Mosul, likely under duress. He was kidnapped with American journalist James Foley in November 2012. An Islamic State group militant beheaded Foley last August.
In this Nov. 11, 2012 file photo, freelance British photojournalist John Cantlie poses with a Free Syrian Army rebel in Aleppo, Syria. (AP Photo, File)
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.
Italian priest Paolo Dall'Oglio on September 25, 2012 in Paris. (KENZO TRIBOUILLARD/AFP/GettyImages)
SAMIR KASSAB: A Lebanese 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.
In this Friday, Nov. 9, 2013 file image made from undated video by Abu Dhabi-based broadcaster Sky News Arabia, Samir Kassab, a Lebanese citizen, poses at an unknown place. (AP Photo/Sky News Arabia, File)
ISHAK MOKHTAR: A Mauritanian reporter for Sky News Arabia. He was kidnapped Oct. 15 while working near Aleppo.
In this image made from an Oct. 20, 2013 file video by Abu Dhabi-based broadcaster Sky News Arabia, Ishak Mokhtar, a Mauritanian national, reports from Syria. (AP Photo/Sky News Arabia, File)
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 RED CROSS: The three 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.
SEVEN LEBANESE SOLDIERS: Abducted in August in the Lebanese border town of Arsal during a cross-border militant raid from Syria.
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.
Italian aid workers abducted in Syria last summer, Greta Ramelli (L) and Vanessa Marzullo arrive at Ciampino airport in Rome early on January 16, 2015 after being freed (FILIPPO MONTEFORTE/AFP/Getty Images)
NICOLAS HAMMARSTROM and MAGNUS FALKEHED: Swedish freelance journalists released in January after about 90 days in captivity. Swedish officials declined to say who seized them or how they were set free.
Swedish journalists Magnus Falkehed (L) and photographer Niclas Hammarstrom address a press conference at the Arlanda Airport north of Stockholm, Sweden on January 9, 2014. (JANERIK HENRIKSSON / TT/AFP/Getty Images)
EDOUARD ELIAS, DIDIER FRANCOIS, NICOLAS HENIN and PIERRE TORRES: French journalists released in April after being held hostage for 10 months.
French President Francois Hollande, third from left, speaks upon arrivals of released French hostages, from left, Didier Francois, Edouard Elias, Nicolas Henin and Pierre Torres, at the Villacoublay military airbase, outside Paris, Sunday, April 20, 2014. (AP Photo/Jacques Brinon)
JAVIER ESPINOSA, RICARDO GARCIA VILANOVA and MARC MARGINEDAS: Spanish journalists released in March after being held hostage for months.
Spanish reporters Javier Espinosa, right, and Ricardo Garcia Vilanova, left, poses upon his arrival at the military airbase in Torrejon de Ardoz, Madrid, Spain, Sunday, March 30, 2014. (AP Photo/Pool)
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