Deep in Syria is the city of Raqqa, considered the de facto capital of Islamic State.

Islamic State billboards are seen along a street in Raqqa, eastern Syria, which is controlled by the Islamic State, October 29, 2014. The billboard reads: "We will win despite the global coalition". (REUTERS/Nour Fourat)

Residents walk along the Tal Abyad street market in central Raqqa, ahead of the upcoming Muslim Eid al-Adha holiday, October 3, 2014.

(REUTERS/Stringer)

Residents walk along the Tal Abyad street market in central Raqqa, ahead of the Muslim Eid al-Adha holiday, in Raqqa, October 3, 2014. (REUTERS/Stringer)

Youths carry banners during a protest against the U.S. airstrikes on the Islamic State in Raqqa, September 26, 2014. The banners in Arabic read, "By the soul, by the blood, we sacrifice ourselves oh state.(REUTERS/Stringer)

Militant Islamist fighters take part in a military parade along the streets of northern Raqqa province, June 30, 2014. (REUTERS/Stringer)

An Islamic State militant uses a loud-hailer to announce to residents of Tabqa city that Tabqa air base has fallen to Islamic State militants, in nearby Raqqa city, August 24, 2014. (REUTERS/Stringer

Residents drive and ride their vehicles through a street in central Raqqa, September 25, 2014. (REUTERS/Stringer)

Fighters from Islamic State in Iraq and the Levant burn confiscated cigarettes in the city of Raqqa, April 2, 2014. (REUTERS/Stringer

Children play on a ride inside a park in Raqqa, September 18, 2014. (REUTERS/Stringer)

A boy stands during a protest against the U.S. airstrikes on the Islamic State (IS) in Raqqa, September 26, 2014. (REUTERS/Stringer)

Female school students wearing a full veil walk along a street in the northern province of Raqqa, March 31, 2014. (REUTERS/Stringer

Residents flee what activists say was an air strike by forces loyal to Syria's President Bashar al-Assad on Tal Abyad street market in central Raqqa, September 6, 2014. (REUTERS/Stringer)

A boy turns his head while standing amongst others praying inside a mosque in Raqqa, September 26, 2014. (REUTERS/Stringer) 

Residents look at fabric inside a shop in Raqqa, September 18, 2014. (REUTERS/Stringer)

An Islamic State militant stands next to residents as they hold pieces of wreckage from a Syrian war plane after it crashed in Raqqa, in northeast Syria, September 16, 2014. (REUTERS/Stringer) 

Militant Islamist fighters take part in a military parade along the streets of Syria's northern Raqqa province, June 30, 2014. (REUTERS/Stringer)

Militant Islamist fighters waving flags, travel in vehicles as they take part in a military parade along the streets of Syria's northern Raqqa province, June 30, 2014. (REUTERS/Stringer)

Men pray outside their shops in Raqqa, April 5, 2014. (REUTERS/Stringer)

An Islamic State policeman controls traffic in Raqqa, September 18, 2014. (REUTERS/Stringer)

Residents swim in the Euphrates River in Raqqa, July 3, 2014. (REUTERS/Stringer)

Militant Islamist fighters ride horses as they take part in a military parade along the streets of Syria's northern Raqqa province, June 30, 2014. (REUTERS/Stringer)

A vendor sells traditional bread during the Muslim holy fasting month of Ramadan in Raqqa province, eastern Syria, which is controlled by the Islamic State, July 23, 2014. (REUTERS/Stringer)

Veiled women walk past a billboard that carries a verse from Koran urging women to wear a hijab in the northern province of Raqqa, March 31, 2014. (REUTERS/Stringer)

Residents carry the body of a man killed by what activists say was an air strike by forces loyal to Syria's President Bashar al-Assad on Tal Abyad street market in central Raqqa, September 6, 2014. (REUTERS/Stringer)

A militant Islamist fighter uses a mobile to film his fellow fighters taking part in a military parade along the streets of Syria's northern Raqqa province, June 30, 2014. (REUTERS/Stringer)

Residents look at gold jewellery displayed at a shop window in Raqqa, September 18, 2014. (REUTERS/Stringer)

A militant Islamist fighter waving a flag, cheers as he takes part in a military parade along the streets of Syria's northern Raqqa province, June 30, 2014. (REUTERS/Stringer)

Children gesture as they stand on a street in Raqqa, September 18, 2014. (REUTERS/Stringer)

Residents flee what activists say was an air strike by forces loyal to Syria's President Bashar al-Assad on Tal Abyad street market in central Raqqa, September 6, 2014. (REUTERS/Stringer)

A resident inspects perfumes inside a shop in Raqqa, September 18, 2014. (REUTERS/Stringer)

A member loyal to the Islamic State in Iraq and the Levant waves an ISIL flag in Raqqa, June 29, 2014. (REUTERS/Stringer) 

Militant Islamist fighters in military vehicles parade along the streets of Syria's northern Raqqa province, June 30, 2014. (REUTERS/Stringer)

A militant Islamist fighter gestures as he takes part in a military parade along the streets of Syria's northern Raqqa province, June 30, 2014. (REUTERS/Stringer)

Residents rest by the Euphrates River in Raqqa, April 11, 2014. (REUTERS/Nour Fourat)

A family sits in a pick-up truck in the Euphrates River in Raqqa, April 11, 2014. (REUTERS/Nour Fourat)

Militant Islamist fighters on a tank take part in a military parade along the streets of northern Raqqa province, June 30, 2014.

(REUTERS/Stringer)

Veiled women sit as they chat in a garden in the northern province of Raqqa, March 31, 2014. (REUTERS/Stringer)

A resident of Tabqa city touring the streets on a motorcycle waves an Islamist flag in celebration after Islamic State militants took over Tabqa air base, in nearby Raqqa city, August 24, 2014. (REUTERS/Stringer)

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