BAGHDAD/BEIRUT (REUTERS) - A convoy of Shi'ite Muslim militia and Iraqi army forces set out from a base near Ramadi on Saturday to advance on areas held by the Islamic State in Iraq and Syria group (ISIS), a Shi'ite spokesman said, launching a counter-offensive to reverse stunning gains by the insurgents.
The fall of Ramadi, the Anbar provincial capital, to ISIS on May 17 could be a shattering blow to Baghdad's weak central government. The Sunni Muslim militants now control most of Anbar and could threaten the western approaches to Baghdad, or even surge south into Iraq's Shi'ite heartland.
Ramadi's loss is the most serious setback for Iraqi forces in almost a year and has cast doubt on the effectiveness of the US strategy of air strikes to help Baghdad roll back ISIS, which holds a third each of Iraq and adjacent Syria.
Anbar provincial council member Azzal Obaid said hundreds of Shi'ite fighters, who had arrived at the Habbaniya air base last week after ISIS took Ramadi, deployed into Khalidiya on Saturday and were approaching Siddiqiya and Madiq, towns in contested territory near Ramadi.
Disadvantaged by poor morale and cohesion among his security forces, Iraqi Prime Minister Haider al-Abadi, a Shi'ite, sent Shi'ite paramilitary groups to try to retake Ramadi despite the risk of inflaming tensions with Anbar's aggrieved, predominantly Sunni population.
Jaffar Husseini, spokesman for the Shi'ite paramilitary group Kataib Hezbollah, said it had deployed more than 2,000 reinforcements which had managed to secure Khalidiya and the road connecting it to Habbaniya.
"Today will witness the launch of some tactical operations that pave the way to the eventual liberation of Ramadi," he told Reuters by telephone.
At the same time, ISIS units have been advancing towards Fallujah to try to absorb more territory between it and Ramadi that would bring them closer to Baghdad, the Iraqi capital, around 80km to the east. A pro-government Sunni tribal leader in the area said on Friday that ISIS forces were around 5km from Khalidiya.
ISIS has controlled Fallujah for more than a year.
A UN spokesman said on Friday that some 55,000 people have fled Ramadi since it was stormed by ISIS earlier this month, with most taking refuge in other parts of Anbar, a vast desert province that borders on Syria, Jordan and Saudi Arabia.
In Syria, ISIS fighters raised their flag over an ancient citadel in the historic city of Palmyra, pictures posted online overnight by the group's supporters showed.
The militants seized Palmyra, known as Tadmur in Arabic and strategically significant with nearby natural gas fields and roads leading south-west to Damascus, on Wednesday after days of heavy fighting with the Syrian army.
"Tadmur citadel under the control of the caliphate," read a caption on one picture posted on social media sites. In another, a smiling fighter is shown carrying the group's black flag and standing on one of the citadel's walls.
It was not possible to verify the images' authenticity.
Palmyra is home to a Unesco World Heritage site, and Syria's antiquities chief has said the insurgents would destroy its 2,000-year-old ruins, including well-preserved Roman temples, colonnades and a theatre, if they took control of them. While hundreds of statues have been taken to safe locations, there are fears for larger monuments that cannot be moved.
ISIS destroyed ancient monuments and antiquities they see as idolatrous in areas of Iraq they captured last year.
Supporters have also posted videos they say show the group's fighters going room to room in government buildings in Palmyra searching for government troops and pulling down pictures of Syrian President Bashar al-Assad and his father.
Some activists have said more than 200 Syrian soldiers died in the battle for the city.
US-led forces have conducted a further 15 air strikes on ISIS positions in Iraq and Syria since Thursday, concentrating on targets near Ramadi, the US military said.