SOUTH OF MOSUL (Reuters) - U.S.-backed Iraqi security forces closing in on the Islamic State-held western half of Mosul launched a major offensive on the city’s airport and fought their way into a nearby military base on Thursday.

Federal police and an elite interior ministry unit known as Rapid Response stormed the airport and engaged in gun battles with Islamic State fighters who used suicide car bombs to try to stem the advance, according to a Reuters correspondent south of Mosul airport.

Police officers told Reuters that the police and Rapid Response forces had taken control of large parts of the airport.

Other officers said the militants deployed bomb-carrying drones to attack 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 from regrouping. It’s the best way to knock them down quickly,” said federal police captain Amir Abdul Kareem, whose units are fighting near Ghozlani military base.

Zohra Bensemra / Reuters Iraqi security forces hope to use the captured airport as a launchpad for other assaults against ISIS.

After ousting the militant group from eastern Mosul last month, Iraqi forces have sought to capture the airport to use it as a launchpad for an onslaught into the west of the city.

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.

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.

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.

Iraqi special forces on the outskirts of western Mosul: pic.twitter.com/Xdf7gahUhw — Mike Giglio (@mike_giglio) February 23, 2017

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.