Remains of Iraqi security forces who were killed by Islamic State militants are seen in Saqlawiya, north of Falluja, Iraq, June 5, 2016. REUTERS/Thaier Al-Sudani TPX IMAGES OF THE DAY - RTSG430

A member of the Iraqi security forces fires artillery during clashes with Islamic State militants near Falluja, Iraq, May 29, 2016. REUTERS/Alaa Al-Marjani TPX IMAGES OF THE DAY - RTX2EOUX

A man returns to his village after it was liberated from Islamic State militants, south of Mosul in Qayyara, Iraq, October 22, 2016. The fumes in the background are from oil wells that were set ablaze by Islamic State militants. REUTERS/Alaa Al-Marjani TPX IMAGES OF THE DAY - RTX2PZNA

A captured Islamic State tank is seen at the Iraqi army base in Qaraqosh east of Mosul, Iraq November 8, 2016. REUTERS/Zohra Bensemra TPX IMAGES OF THE DAY - RTX2SIUR

People run in panic after a coalition airstrike hit Islamic State fighters positions in Tahrir neighbourhood of Mosul, Iraq, November 17, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTX2U4B2

A Syria Democratic Forces (SDF) fighter helps civilians who were evacuated by the SDF from an Islamic State-controlled neighbourhood of Manbij, in Aleppo Governorate, Syria, August 12, 2016. The SDF has said Islamic State was using civilians as human shields. REUTERS/Rodi Said - RTSMZE7

A member of Iraqi government forces celebrate along a street in Falluja after government forces recaptured the city from Islamic State militants, Iraq, June 27, 2016. REUTERS/Thaier Al-Sudani - RTX2II1Z

A U.S. fighter stands near a military vehicle, north of Raqqa city, Syria November 6, 2016. REUTERS/Rodi Said - RTX2S5R8

Iraqi special forces soldiers fire weapons at Islamic State fighters in Mosul, Iraq November 14, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTX2TKQ4

Fighters of Libyan forces allied with the U.N.-backed government fire a rocket at Islamic State fighters in Sirte, Libya, August 4, 2016. REUTERS/Goran Tomasevic - RTSL2UE

Syria Democratic Forces (SDF) female fighters embrace each other in the city of Manbij, in Aleppo Governorate, Syria, August 10, 2016. REUTERS/Rodi Said - RTSMDAL

An Islamic State suicide bomber attacks Iraqi special forces soldiers with a car bomb during clashes in Mosul, Iraq, November 19, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTSSDHT

An Iraqi soldier is pictured during an operation against Islamic State militants in the frontline neighbourhood of Intisar, eastern Mosul November 27, 2016. REUTERS/Mohammed Salem TPX IMAGES OF THE DAY - RTSTIFC

A fighter of the Syria Democratic Forces walks inside a shelter in northern province of Raqqa, Syria May 27, 2016. REUTERS/Rodi Said - RTX2EIZR

Burnt out prison cells belonging to Islamic State militants are seen in Falluja after government forces recaptured the city from Islamic State militants, Iraq, June 27, 2016. REUTERS/Thaier Al-Sudani TPX IMAGES OF THE DAY - RTX2IIXN

Iraqis who fled violence in Mosul gather as they reach Syria, near the Iraqi border, in Hasaka Governorate October 20, 2016. REUTERS/Rodi Said - RTX2PS8R

A detained man accused of being an Islamic State fighter sits in front of newly displaced men near a check point in Qayyara, east of Mosul, Iraq October 26, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTX2QJG9

Members of an Iraqi special forces police unit fire their weapons at Islamic State fighters in al-Shura, south of Mosul, Iraq October 29, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTX2QYZX

A Kurdish Peshmerga fighter looks over Mosul from his position near Abu Jarboa village, Iraq November 1, 2016. REUTERS/Ahmed Jadallah - RTX2RCNX

Men pull with a rope the body of an Islamic State fighter before burying him near Karamah, south of Mosul, Iraq November 11, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTX2T6VW

A man carries his belongings after he crossed from an Islamic State fighters-controlled part of Mosul into an Iraqi special forces soldiers-controlled part of Mosul, Iraq November 14, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTX2TKYN

A man cries over a body of a baby killed by a mortar round fired by Islamic State fighters in Mosul, Iraq, November 16, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTX2TXZV

An Iraqi special forces soldier takes cover behind a humvee during an Islamic State fighter car bomb suicide attack in Tahrir neighbourhood of Mosul, Iraq, November 17, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTX2U3R8

Rebel fighters search men who fled from Islamic State-controlled areas, upon their arrival in the northern Syrian rebel-held town of Waqf, near al-Rai town, in Aleppo Governorate, Syria, September 29, 2016. Picture taken September 29, 2016. REUTERS/Khalil Ashawi TPX IMAGES OF THE DAY - RTSQWQC

An Iraqi soldier uses his rifle to hold up a helmet as a decoy during clashes with Islamic State fighters in Al-Qasar, South-East of Mosul, Iraq November 28, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTSTQY7

Smoke rises at Islamic State militants' positions in the town of Naweran near Mosul, Iraq, October 23, 2016. REUTERS/Azad Lashkari TPX IMAGES OF THE DAY - RTX2Q1MA

The skin on five-year-old Doaa's arms and neck is blackened after a rocket fired by Islamic State landed and exploded in Qayyara, Iraq, November 12, 2016. REUTERS/Air Jalal TPX IMAGES OF THE DAY - RTX2TCRG