Iraqi forces have made significant advances around Ramadi and an operation to retake the city captured by ISIS group in May is looming, officers said Wednesday.

"Great people, the hour of victory against the Daesh (ISIS) criminal gangs has come," said a statement from the Joint Operations Command for Anbar province, of which Ramadi is the capital.

"Your heroic forces are advancing steadily from the northern side... they managed to reach Albu Farraj area," on the northern edge of the city centre, it said.

The head of the Anbar command, Major General Ismail Mahalawi, told AFP that "Iraqi forces have raised the Iraqi flag on Albu Farraj bridge", over the Euphrates.

Since the start of October, Iraqi forces have been closing in on Ramadi, gaining ground west and north of the city in particular.

ISIS fighters took Ramadi, about 100 kilometres (60 miles) west of Baghdad, in mid-May after a three-day blitz of massive suicide car and truck bomb attacks that forced a disorderly retreat by pro-government troops.

After the most stinging setback suffered by Iraqi forces since they started a counter-offensive to regain the territory lost in mid-2014, officials vowed to swiftly retake Ramadi.

Progress has been sluggish, however, with Iraqi forces and the US-led coalition supporting them in Anbar blaming a number of factors, including searing summer temperatures.

The US-led coalition's spokesman in Baghdad, Colonel Steve Warren, conceded two weeks ago there had been an "operational pause" in efforts to retake Ramadi.

But on Tuesday he said Iraqi forces were now ready to launch an operation inside the city.

"We now believe that battlefield conditions are set for the ISF (Iraqi security forces) to push into the city," he said, estimating between 600 and 1,000 the number of IS fighters remaining in Ramadi.

According to the daily tallies provided by the US military, 58 air strikes have been carried out by coalition warplanes in the Ramadi area since the start of October.

Four were conducted on Tuesday, a statement said.

They "destroyed five ISIL buildings, five ISIL fighting positions, an ISIL tactical vehicle, two ISIL improvised explosive clusters used as minefields, and denied ISIL terrain at three separate locations," it said, using another acronym for ISIS.

The forces battling ISIS around Ramadi are mostly from the regular security forces, including the army, the police and the elite counter-terrorism services.

Thousands of Sunni tribal fighters from Ramadi and elsewhere in Anbar are also active on that front.

Other paramilitary outfits operating under the umbrella of the Hashed al-Shaabi, dominated by Shia militia groups, have focused their efforts around Fallujah, which is still under IS control and lies about half way between Ramadi and Baghdad.

Army and Hashed fighters also launched a broad offensive on Wednesday aimed at reviving efforts to recapture Baiji, a town about 200 kilometres (120 miles) north of Baghdad and the nearby refinery.

The refinery, the country's largest is thought to have been damaged beyond repair by almost non-stop fighting since the first days of the offensive ISIS launched across Iraq in June 2014.

Control of Baiji is also considered a key step towards isolating key IS bastions from one another.