ISIS seized control of the city of Ramadi Sunday, sending Iraqi forces racing out of the city in a major loss despite the support of US-led airstrikes targeting the extremists.
Online video showed Humvees, trucks and other equipment purportedly speeding out of Ramadi, with some soldiers gripping onto their sides.
Prime Minister Haider al-Abadi ordered security forces not to abandon their posts across Anbar province, apparently fearing the extremists could capture the entirety of the vast Sunni province that saw intense fighting after the 2003 US-led invasion of the country to topple dictator Saddam Hussein.
The retreat recalled the collapse of Iraqi police and military forces last summer, when ISIS' initial blitz into Iraq saw it capture about a third of the country. It also calls into questions American officials hopes of relying solely on airstrikes to support the Iraqi forces in expelling the extremists.
"Ramadi has fallen," said Muhannad Haimour, a spokesman for the governor of Anbar province. "The city was completely taken... It was a gradual deterioration. The military is fleeing."
Earlier Sunday, Abadi also ordered Shiite militias to prepare to go into the Sunni-dominated Anbar province, ignoring worries their presence could spark sectarian bloodshed apparently over fears the extremists could seize more territory.
The final push by the extremists began earlier Sunday, when police and army officials said four nearly simultaneous bombings targeted police officers defending the Malaab district in southern Ramadi, killing 10 and wounding 15. Among the dead was Col. Muthana al-Jabri, the chief of the Malaab police station, they said.
Later on, police said three suicide bombers drove their explosive-laden cars into the gate of the Anbar Operation Command, the military headquarters for the province, killing five soldiers and wounding 12.
Fierce clashes erupted between security forces and ISIS militants following the attacks. ISIS militants later seized Malaab after government forces withdrew, with the militants saying they now held the military headquarters.
A police officer who was in Malaab said retreating forces left behind about 30 army vehicles and weapons that included artillery and assault rifles. He said some two dozen police officers also went missing during the fighting.
All the officials spoke on condition of anonymity as they weren't authorized to talk to journalists.
On a militant website frequented by ISIS members, a message from the group claimed its fighters held the 8th Brigade army base, as well as tanks and missile launchers left behind by fleeing soldiers. The message, while it could not be independently verified by The Associated Press, was similar to others released by the group and was spread online by known supporters of the extremists.
The new setback came only a day after Baghdad's decision to send reinforcements to help its battered forces in Ramadi.
Abadi's comments were carried on state television, which did not elaborate on the situation in Ramadi or elsewhere in Anbar province. Iraqi warplanes also launched airstrikes on ISIS positions inside Ramadi on Sunday, the Iraqi Defense Ministry said, without elaborating.
Later, the military issued a statement also calling on its forces not to abandon Anbar province.
"Victory will be in the side of Iraq because Iraq is defending its freedom and dignity," the military said. It did not offer any details about the ongoing fighting.
Last week, the militants swept through Ramadi, seizing the main government headquarters and other key parts of the city. It marked a major setback for the Iraqi government's efforts to drive the militants out of areas they seized last year. Previous estimates suggested ISIS held at least 65 percent of the vast Anbar province.
Backed by US-led airstrikes, Iraqi forces and Kurdish fighters have made gains against ISIS, including capturing the northern city of Tikrit. But progress has been slow in Anbar, a Sunni province where anger at the Shiite-led government runs deep and where US forces struggled for years to beat back a potent insurgency. American soldiers fought some of their bloodiest battles since Vietnam on the streets of Fallujah and Ramadi.
US troops were able to improve security in the province starting in 2006 when powerful tribes and former militants turned against al-Qaeda in Iraq, a precursor to ISIS, and allied with the Americans.
But the so-called Sunni Awakening movement waned in the years after US troops withdrew at the end of 2011, with the fighters complaining of neglect and distrust from the Shiite-led government in Baghdad.
The US-led coalition said Sunday it conducted seven airstrikes in Ramadi in the last 24 hours, as well as three in Fallujah.
"It is a fluid and contested battlefield," said Army Col. Steve Warren, a Pentagon spokesman. "We are supporting (the Iraqis) with air power."