Iraqi forces have pushed into the southern edge of Fallujah, enduring car bombs and sniper fire from Isis fighters determined to hold onto the strategic western city.
Lieutenant General Abdulwahab al-Saedi, commander of the offensive, said forces from Iraq's Army, police and Counterterrorism Service launched the assault on southern Fallujah yesterday.
Since Prime Minister Haider al-Abadi announced the operation just over a week ago, government forces, together with Shia militia troops and tribal fighters, mostly from Sunni Anbar province, have taken territory around Fallujah in preparation for an assault on its urban area.
"Forces are still advancing, and clashes are ongoing," Saedi told state television.
Capturing Fallujah, the first Iraqi city to fall to Isis (Islamic State) in 2014, is expected to be both an important battle and a difficult one. The city, about 70km west of Baghdad, is known for its history of nurturing armed Islamist groups.
In 2004, US Marines fought two fierce battles to take control of Fallujah, but insurgents returned each time.
Saedi said the government forces were approaching the Shuhadaa neighbourhood in southern Fallujah. Speaking later to the Washington Post, he said militants detonated at least two car bombs and were using snipers and rockets to fend off advancing troops.
"The Counterterrorism Service forces have the experience to fight them, just like they did in Ramadi, Hit and Rutba," Saedi said, referring to other recent battles.
Military officials said the forces had not entered the city proper.
North of Fallujah, federal police, soldiers and militia pressed into the town of Saqlawiya, while police raised the Iraqi flag over the police station in Na'imiyah south of the city. The Iraqi military also said its warplanes had launched attacks on Isis positions around Fallujah and American aircraft were also conducting strikes.
Lieutenant Colonel Abdul Ghani al-Assadi, commander of the Counterterrorism Service, said Fallujah was a complicated operation, because of its history of supporting insurgents and because the battle would unfold in an area with a significant civilian population.
Lieutenant General Sean MacFarland, the US commander in Iraq, warned last week that government forces may have to contend with Isis sympathisers among the local population.
Reasserting government control of Fallujah would deal a major blow to the group in western Iraq, where it has been able to draw strength from fellow militants in neighbouring Syria. The Counterterrorism Service troops are expected to play a key role in leading the charge into the heart of Fallujah, as they have in other battles.
Saedi said security forces attacked from southern Fallujah because it was largely empty of civilians. About 50,000 civilians are believed to be in Fallujah, where conditions have worsened as basic supplies grow scarce.
Mayor Issa al-Issawi said that civilians had begun to move from southern areas of Fallujah towards the north, and may be used by militants as human shields.
He said there had been reports of civilian casualties from recent shelling and air operations by government-aligned forces. Some residents have been killed by militants while trying to flee, officials from the city have said. The Washington Post could not independently confirm those reports.
Officials believe a recent surge in terrorist bombings in the Iraqi capital reflects an effort by Isis to divert government attention from the battlefield. Authorities are hoping that recapturing Fallujah would reduce that threat.