They were always seen as the key to defeating the jihadists in their bastions but the fall of Ramadi has deepened the distrust that Iraq's Sunni tribes feel towards the government.

Many tribal leaders in Anbar province, of which Ramadi is the capital, said they would continue to fight the Islamic State group, not for the sake of a government they say never offered the adequate support, but because they have no other choice.

"The fall of Ramadi is a disaster," said Salah Hassan al-Nada, a tribal leader from Awja, near the northern city of Tikrit, who moved to Kurdistan when IS established its grip on Sunni areas last year.

"Ramadi truly was a model," he said, in reference to the force of tribal fighters called "Sahwat" (Awakening) that emerged a decade ago to battle previous incarnations of IS.

"They are the ones who fought them and kicked them out of Ramadi and brought normal life back to the city," he said.

The force spread to several parts of Iraq to reach a strength of around 50,000 men initially paid directly by the United States.

Responsibility was transferred to the government in 2008 and the outfit was eventually disbanded after relations soured over former prime minister Nuri a-Maliki's failure to deliver on promises to integrate the Sahwat in the army.

His successor Haider al-Abadi has only just begun to rekindle the Sahwat under a different and more controlled format, by incorporating them into the Shiite-dominated Hashed al-Shaabi organisation that serves as an umbrella for volunteers and militias.

In 2014, the remnants of the extremist groups the tribes had successfully fought returned as the most violent organisation in modern jihad, and this time with more ambitious goals than insurgency warfare.

As IS seized territory and proclaimed a "caliphate" that has drawn thousands of foreigners but also been seen by some Iraqis as a lesser evil than sectarian Shiite rule, the tribes that did oppose the jihadists felt they were not getting nearly enough backing.

"The tribes of Anbar did not fail facing Daesh, it's the government that failed because it fears that arming the tribes will turn against it," Anbar tribal sheikh Omar al-Alwani said, using an Arab acronym for IS.

He argued that the tribes could have defeated IS without the Hashed had they been provided heavier weaponry.

- Political solution -

Victoria Fontan, a professor at American University Duhok Kurdistan, said trust will be difficult to rebuild without a political solution.

"Morale is now very low among the Sunnis after what happened in Ramadi," she said.

The Shiite-dominated government is blaming Anbaris for not mobilising en masse against IS.

"However, it is difficult for Sunnis to actually support the government against IS, since the government has been dropping barrel bombs on them," Fontan said.

The previous government carried out air raids, mainly in the Fallujah area of Anbar, using barrel bombs -- improvised, unguided devices packed with explosives and scrap metal known for causing indiscriminate damage.

"If Baghdad promises autonomy to Sunni regions in exchange for their support against IS, that will be a game changer. A political solution is the only way to actually derail IS for good in Iraq," she argued.

Michael Knights of the Washington Institute was more hopeful that Baghdad and the Sunni tribes could work together effectively.

"Sunni tribal groups simply will not be able to operate independently against armoured IS suicide truck bombs without anti-tank capabilities," he wrote in analysis for the think-tank, which focuses on US Middle East policy.

"The quickest and least controversial way to protect them is by embedding them in existing units," he said.

For Ashour al-Mihlawi, a tribal leader from Ramadi's Albu Mihl tribe, Anbaris can only count on themselves.

"If the government responds to the tribes' requests, especially those who fought Daesh and Al-Qaeda, our relations will be good... If it doesn't, we will never trust it," he said.

"We will not join Daesh, we will fight it by ourselves with the means that we have."

IS attacks Iraq forces east of Ramadi: officials
Baghdad (AFP) May 21, 2015 - The Islamic State group seized positions from Iraqi security forces east of Ramadi Thursday as it tried to keep its momentum after capturing the city, officials said.

The jihadists pressed their offensive along the Euphrates to attack positions held by the government in Husaybah, seven kilometres (4.5 miles) east of Anbar's provincial capital.

"Daesh took control of the defence lines in Husaybah al-Sharkiya, where the security forces were supposed to launch their operations to liberate Ramadi," a police colonel said.

Daesh is an Arab acronym for the IS, which scored its biggest victory in Iraq in almost a year when it took over Ramadi on Sunday.

He said the positions lost on Thursday were meant to protect Khaldiyah, Habbaniyah and a major nearby military base.

"Daesh was able to penetrate 500 metres (yards) into the area. There are fierce clashes between the security forces and the attackers," the police officer said, speaking on condition of anonymity.

Rafia Abdelkarim al-Fahdawi, a local tribal leader, confirmed that the government defence positions in Husaybah had been lost and said the jihadists now threatened to take the entire area.

"We fear there might be a massacre of the sons of the Albu Fahd tribe if Daesh takes full control," said Fahdawi, whose tribe has been fighting alongside the government against IS.

Prime Minister Haider al-Abadi called in the Popular Mobilisation (Hashed al-Shaabi) forces, an umbrella organisation mostly of Shiite militias and volunteers, after Ramadi fell.

Reinforcements have arrived at Habbaniyah and other locations in Anbar but no operation to retake Ramadi -- 100 kilometres (60 miles) west of Baghdad -- has yet begun in earnest.

A swift counter-attack is key to preventing IS from planting explosive devices across Ramadi, which would make a government advance more risky and complicated.

Michael Knights, of the Washington Institute think tank, also said the government and its allies should waste no time in putting IS on the back foot in Ramadi to deny it more control of eastern Anbar.

"The Iraqi government needs to put ISIS on the defensive in eastern Anbar before Ramadan begins in mid-June, when the terrorist movement will no doubt try to surge attacks against Shiite religious and civilian targets in Baghdad and the shrine city of Karbala," he said.

IS already controls most of Anbar, a vast province which stretches from the Saudi, Jordan and Syria borders all the way east to the outskirts of Baghdad.