By Ahmed Rasheed
BAGHDAD, Oct 29 (Reuters) - Iraqi security forces said they advanced to within 2 km (1.2 mile) of the city of Baiji on Wednesday in a new offensive to retake the country's biggest oil refinery that has been besieged since June by Islamic State militants.
Backed by Shi'ite militias and army helicopters, government forces have swept through a desert area to the west of Baiji, aiming to recapture the city 200 km (130 miles) north of the capital.
They hope to cut off supply lines to militants encircling the refinery and gain control of a road leading to the city of Mosul, an army colonel told Reuters.
Islamic State fighters swept through northern Iraq in June, seizing the city of Baiji and surrounded the sprawling refinery.
Since then, government forces inside the refinery complex have been surrounded by the Sunni insurgents who have failed to take it despite frequent attacks and suicide bombings.
"We have made good advances. We have taken over six villages and now we are only 2 km away from the city of Baiji," said the colonel, who requested anonymity.
Islamic State has used roadside bombs and snipers to slow down the government forces' progress.
"Since yesterday morning we have defused 300 roadside bombs planted by the terrorists to delay our advance," the colonel said.
The Baiji refinery was producing around 175,000 barrels per day before it was closed, a senior Iraqi official said in June. Iraq's domestic daily consumption is estimated at 600,000-700,000 bpd.
Iraqi security forces said they had gained momentum elsewhere over the last week, retaking the town of Jurf al-Sakhar, just south of Baghdad.
Government troops also retook parts of the Himreen Mountains overlooking Islamic State supply lines north of the capital, said another army colonel.
These accounts of government advances could not immediately be independently confirmed.
The gains have not eased violence across the country reminiscent of a civil war that peaked in 2006-2007.
Sunnis accuse Shi'ite militias of kidnapping, torturing and killing members of their minority sect with impunity, charges they reject.
Shi'ite militias say they are tracking down Islamic State militants who are living among Sunnis.
On Wednesday, roadside bombs killed four people in and around Baghdad and a police major was assassinated in the western part of the capital when an explosive device attached to his vehicle exploded, police and hospital sources said.
Kurdish peshmerga fighters have also been battling Islamic State in the north, where they have made progress backed by U.S. air strikes.
Iraqi peshmerga arrived in southeastern Turkey early on Wednesday ahead of their planned deployment to the Syrian town of Kobani to help fellow Kurds repel an Islamic State advance which has defied U.S.-led air strikes. (Writing by Michael Georgy; Editing by Robin Pomeroy and Giles Elgood)