Libyan forces allied with the U.N.-backed government fire artillery towards IS fighters positions in Sirte, Libya, July 12, 2016. REUTERS/Goran Tomasevic TPX IMAGES OF THE DAY - RTSHM7N

Libyan forces allied with the U.N.-backed government fire artillery towards IS fighters positions in Sirte, Libya, July 12, 2016. REUTERS/Goran Tomasevic - RTSHM7O

Libyan forces allied with the U.N.-backed government fire weapons at Islamic State fighters in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI55I

Libyan forces allied with the U.N.-backed government move with a tank towards Islamic State fighters' positions in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI536

Libyan forces allied with the U.N.-backed government fire weapons during a battle with Islamic State fighters in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI542

Libyan forces allied with the U.N.-backed government look at Islamic State fighters' positions before a battle in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI555

A member of the Libyan forces allied with the U.N.-backed government fires his gun at Islamic State fighters during a battle in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI557

Libyan forces allied with the U.N.-backed government play table football at the frontline in the West part of Sirte, Libya, July 19, 2016. REUTERS/Goran Tomasevic - RTSIP1Q

Libyan forces allied with the U.N.-backed government fire weapons during a battle with Islamic State fighters in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI5CL

A member of Libyan forces allied with the U.N.-backed government fires his gun at Islamic State fighters during a battle in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI530

A member of Libyan forces allied with the U.N.-backed government fires his gun at Islamic State fighters during a battle in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI537

A fighter of the Libyan forces allied with the U.N.-backed government walks in a house located at the frontline in the West part of Sirte, Libya, July 19, 2016. REUTERS/Goran Tomasevic - RTSIP1J

Libyan forces allied with the U.N.-backed government look at Islamic State fighters' positions in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI55E

A member of Libyan forces allied with the U.N.-backed government gestures during a battle with Islamic State fighters in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI544

Libyan forces allied with the U.N.-backed government fire weapons during a battle with Islamic State fighters in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI53Z

A member of the Libyan forces allied with the U.N.-backed government looks at Islamic State fighters' positions during a battle in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI55F

Libyan forces allied with the U.N.-backed government look at Islamic State fighters' positions before a battle in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI535

Libyan forces allied with the U.N.-backed government fire weapons during a battle with Islamic State fighters in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI556

Libyan forces allied with the U.N.-backed government look at the positions of Islamic States fighters in the West part of Sirte, Libya, July 19, 2016. REUTERS/Goran Tomasevic - RTSIP1R

A member of the Libyan forces allied with the U.N.-backed government looks at Islamic State fighters' positions in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI55C

Libyan forces allied with the U.N.-backed government fire weapons as they move towards Islamic State fighters' positions in Sirte, Libya, July 15, 2016. REUTERS/Goran Tomasevic - RTSI532

A member of the Libyan forces allied with the U.N.-backed government takes a break at the frontline in Sirte, Libya, July 18, 2016. REUTERS/Goran Tomasevic - RTSII5S