Iraqi forces have recaptured the main government complex in Ramadi held by Islamic State (ISIS) since May, a day after the extremist group's leader said in a rare audio address that recent setbacks hadn't weakened the militants.

The reversal in Ramadi, located about 110 kilometers (68 miles) west of Baghdad, came after U.S. and coalition aircraft recently stepped up their bombing of Islamic State positions, including four airstrikes near the city on Saturday targeting vehicles, weaponry and tactical staging areas.

ISIS fighters fled the Ramadi complex, which they had been using as a headquarters, with the arrival of Iraqi troops, CNN and Reuters reported citing Iraqi government sources.

"The forces of the counter-terrorism unit are now controlling the government compound," Sabah Noori, a spokesman for the Iraqi special forces, told the Washington Post. Pockets of Islamic State resistance are said to remain in the city.

A defeat in Ramadi would mark another step in attempts to reverse Islamic State's momentum in OPEC's second-largest producer, following the recapture of Tikrit earlier this year. It would be a comeback of sorts for Iraq's troops, criticized by U.S. Defense Secretary Ashton Carter as having had "no will to fight" when Islamic State overran the city in May.

Paris Attacks

Airstrikes by the U.S.-led coalition were intensified after the militant group claimed responsibility for the Paris terror attacks in November, which killed 130 people and injured hundreds more.

U.S. and coalition aircraft, including fighter jets and drones, conducted five strikes on Islamic State positions in Syria and 28 in Iraq on Saturday alone, the U.S. Department of Defense said. Initial reports showed that among the items destroyed were weapons, explosive caches, bridges, bunkers and vehicles, the DOD said in a statement.

Saturday's audio message, which appeared on social media accounts and websites used by Islamic State, was the first to purportedly come from Islamic State's Abu Bakr al-Baghdadi since May. Baghdadi said his group had sustained setbacks before before in Iraq and Syria, only to return stronger.

Israel Threat

He also addressed Israel, saying: "Palestine will only be your graveyard." That first explicit threat to Israel echoed a typical rallying cry used by Arab leaders for more than six decades.

Baghdadi's threat to Israel may reflect an attempt to garner support in the region by targeting a "common cause," according to Sultan Barakat, director of research at the Brookings Doha Center. 

Islamic State has declared a caliphate in areas of Syria and Iraq it has seized. The U.S. is undertaking a significant effort to find and kill Baghdadi, who is in hiding, an Obama administration official said earlier this month.

The U.S. has promised to send additional special forces to Iraq and Syria to combat the group. U.S. officials have said aerial bombing alone can't defeat Islamic State, and that ground forces are needed. Baghdadi said the U.S. and its allies wouldn't dare to send ground forces to fight Islamic State after being bogged down in lengthy conflicts in Afghanistan and Iraq.

Baghdadi was also dismissive of a newly announced Islamic alliance against terrorism, led by Saudi Arabia.

"If this coalition was Islamic, it would have staged a war against the Alawites and the Russians in Syria, it would have announced war against the Shiites and the Kurds in Iraq," Baghdadi said, calling on Saudi citizens to join Islamic State.