Iraqi government forces retook four villages on Sunday near a mountain ridge overlooking Islamic State supply lines, security officials said, in a campaign which has struggled to make advances against the Sunni Islamist insurgents.

Iraqi security forces backed by Shi'ite militias gained some momentum on Saturday in their bid to loosen the grip of Islamic State, which controls large swathes of territory in the north and west of the country.

After months of fighting they drove Islamic State militants out of Jurf al-Sakhar, just south of Baghdad, while Kurdish fighters regained control over the town of Zumar in the north.

Sunni insurgents have been moving fighters, weapons and supplies from western Iraq through secret desert tunnels to Jurf al-Sakhar, Iraqi officials have said. Now it appears government forces may be able to disrupt that network.

Iraqi security forces backed by Shi'ite militias launched an assault on Saturday on areas around the Himreen mountains, a hotbed of militant activity 100 km (60 miles) south of the oil city of Kirkuk.

On Sunday they seized control of four villages in the area, security officials said, adding that it was very difficult to accelerate efforts to capture more territory because of roadside bombs and booby-trapped houses.

"We have decided to make slow advances. We hold the ground, set up watch towers, clear the explosives and build sand barriers to prevent the armed men from returning," army major Ahmed Nu'aman told Reuters by telephone.

PROTRACTED FIGHTING

The operation is designed to isolate Islamic State fighters controlling the towns of Jalawla and Saadiya and cut off the areas they seized northeast of the city of Baquba, which is held by Iraqi security forces and Shi'ite militias.

Government forces and Kurdish peshmerga fighters have been trying for months to take over Jalawla and Saadiya, located northeast of Baghdad.

Islamic State swept through northern Iraq in the summer, facing little resistance from US-trained government troops.

The al Qaeda offshoot then declared a caliphate and threatened to march on Baghdad, rattling the Shi'ite-led government and intensifying sectarian bloodshed.

While US airstrikes on Islamic State targets in Iraq and Syria may have disrupted their operations, it is hard to tell whether the campaign can defeat the insurgents who want to redraw the map of the Middle East.

Much may depend on whether the performance of Iraq's army and security forces improves.

On Sunday, a suicide bomber in a truck packed with explosives killed three soldiers at an Iraqi army gathering on a highway west of former Iraqi president Saddam Hussein's home town of Tikrit, military sources said.

Government forces and Shi'ite militias also attempted to advance on a village near Tikrit held by Islamic State, the sources said. But they failed in the face of roadside bombs, landmines and sniper fire. Clashes raged in the area all day.

The next major security operation is expected to target the town of Amriyat al-Falluja, located in the Sunni heartland of Anbar province, just 40 km (25 miles) from Baghdad.

The Sunni insurgents have been surrounding it for weeks. Security officials said government forces are preparing to try and break the siege, security officials said.

Islamic State fighters also appear to be gearing up for battle.

Militants in the nearby town of Falluja, an Islamic State bastion and former al Qaeda stronghold under the US occupation of Iraq, used loudspeakers attached to police vehicles they captured to address supporters.

They were told to expect good news from Amriyat al-Falluja.

"Don't be afraid. Don't worry about what happened in Jurf al-Sakhar. The mujahideen will be back," was the message conveyed over loudspeakers, a witness told Reuters from Falluja.

"Be cheerful. We have 100 suicide bombers preparing for the battle of Amriyat al-Falluja and we have more if the situation warrants." – Reuters