By Isabel Coles and Stephen Kalin

SOUTH OF MOSUL (Reuters) – U.S.-backed Iraqi security forces captured Mosul airport on Thursday, state television said, in a major gain in operations to drive Islamic State from the western half of the city.

Elite Counter Terrorism forces advanced from the southwestern side and entered the Ghozlani army base along with the southwestern districts of Tal al-Rumman and al-Mamoun.

Losing Mosul could spell the end of the Iraqi side of militants’ self-styled caliphate in Iraq and Syria, which Islamic State leader Abu Bakr al-Baghdadi declared from the city after sweeping through vast areas of Iraq in 2014.

Iraqi forces hope to use the airport as a launchpad for their campaign to drive the militants from Iraq’s second largest city.

A Reuters correspondent saw more than 100 civilians fleeing towards Iraqi security forces from the district of al-Mamoun. Some of them were wounded.

“Daesh fled when counter terrorism Humvees reached al-Mamoun. We were afraid and we decided to escape towards the Humvees,” said Ahmed Atiya, one of the escaped civilians said, referring to Islamic State by its Arabic name.

“We were afraid from the shelling,” he added.

Federal police and an elite interior ministry unit known as Rapid Response had battled their way into the airport as Islamic State fighters fought back using suicide car bombs, a Reuters correspondent in the area south of Mosul airport said.

Police officers said the militants had also deployed bomb-carrying drones against the Iraqi Counter Terrorism Forces advancing from the southwestern side of the city.

“We are attacking Daesh (Islamic State) from multiple fronts to distract them and prevent them regrouping,” said federal police captain Amir Abdul Kareem, whose units are fighting near Ghozlani military base. “It’s the best way to knock them down quickly.”

NARROW ALLEYWAYS

Western advisers supporting Iraqi forces were seen some 2 km (one mile) away from the frontline to the southwest of Mosul, a Reuters correspondent said.

Iraqi forces last month ousted Islamic State from eastern Mosul and embarked on a new offensive against the militant group in densely-populated western Mosul this week.

The campaign involves a 100,000-strong force of Iraqi troops, Kurdish fighters and Shi’ite militias and has made rapid advances since the start of the year, aided by new tactics and improved coordination.

U.S. special forces in armored vehicles on Thursday positioned near Mosul airport looked on as Iraqi troops advanced and a helicopter strafed suspected Islamic State positions.

Counter-terrorism service (CTS) troops fought their way inside the nearby Ghozlani base, which includes barracks and training grounds close to the Baghdad-Mosul highway, a CTS spokesman told Reuters.

The airport and the base, captured by Islamic State fighters when they overran Mosul in June 2014, have been heavily damaged by U.S.-led air strikes intended to wear down the militants ahead of the offensive, a senior Iraqi official said.

The U.S. military commander in Iraq has said he believes U.S.-backed forces will retake both of Islamic State’s urban bastions – the other is the Syrian city of Raqqa – within the next six months, which would end the jihadists’ ambitions to rule and govern significant territory.

Iraqi commanders expect the battle to be more difficult than in the east of Mosul, however, in part because tanks and armored vehicles cannot pass through narrow alleyways that crisscross the city’s ancient western districts.

Militants have developed a network of passageways and tunnels to enable them to hide and fight among civilians, melt away after hit-and-run operations and track government troop movements, according to inhabitants.

(Additional reporting by Ahmed Rasheed; Writing by Tom Finn and Sami Aboudi; Editing by Ralph Boulton and Dominic Evans)