SINJAR, Iraq --Kurdish Iraqi fighters, backed by U.S.-led airstrikes, launched a major assault Thursday aiming to retake the strategic town of Sinjar, which the Islamic State group overran last year in an onslaught that caused the flight of tens of thousands of Yazidis and first prompted the United States to launch the air campaign against the militants.
Hours into the operation, the Kurdish Regional Security Council said forces were in control of a section of Highway 47, of one of IS's most active supply lines.
The advance completely isolates members of the IS group in Sinjar from militant strongholds in Syria and northern Iraq. The Kurdish fighters also said they had secured the villages of Gabarra, on the western front, and Tel Shore, Fadhelya and Qen on the eastern front.
Some 7,500 peshmerga fighters were closing in on Sinjar from three fronts, the security council said in a statement. In addition to taking the town and the highway, Operation Free Sinjar aimed to establish "a significant buffer zone to protect the city and its inhabitants from incoming artillery."
Heavy gunfire broke out early Thursday as peshmerga fighters began their approach amid aerial bombardment. An Associated Press team saw a small American unit at the top of a hill along the front line, calling in and confirming airstrikes.
The coalition said 24 airstrikes were carried out over the past day, striking nine militant tactical units, nine staging areas and destroying 27 fighting positions, among other targets. Coalition aircraft have conducted more than 250 airstrikes over the past month across northern Iraq.
The Peshmerga "troops are holding their position, waiting for reinforcements and more airstrikes so they can then move into the center of the town. Airstrikes have been very important to the operation getting to the point where it is now," said Maj. Gen. Seme Busal, commander of one of the front lines.
Sinjar was captured by the Islamic State group in August 2014 shortly after the extremists seized Iraq's second-largest city, Mosul, and blitzed across northern Iraq.
The major objective of the offensive is to completely cut off Highway 47, which passes by Sinjar and indirectly links the militants' two biggest strongholds - Raqqa in Syria and Mosul in northern Iraq - as a route for goods, weapons and fighters. Coalition-backed Kurdish fighters on both sides of the border are now working to retake parts of that corridor.
"By controlling Highway 47, which is used by Daesh to transport weapons, fighters, illicit oil, and other commodities that fund their operations, the coalition intends to increase pressure ... and isolate their components from each other," a coalition statement said Thursday, referring to the group by its Arabic acronym.
Iraqiyya state television said Kurdish peshmerga troops also reached the Sinjar mayor's office, though Kurdish officials did not immediately confirm it.
Kurdish officials said clouds of smoke above Sinjar on Thursday were making it more difficult for coalition planes to carry out airstrikes as thousands of peshmerga fighters moved toward the town from the east and west and massed at the edges.
Warplanes in the U.S.-led coalition have been striking around Sinjar ahead of the offensive and strikes grew more intense at dawn Thursday. But Sinjar, located at the foot of Sinjar Mountain about 30 miles (50 kilometers) from the Syrian border, is not an easy target. One attempt by the Kurds to retake it stalled in December. The militants have been reinforcing their ranks in Sinjar recently in expectation of an assault, though the U.S.-led coalition was not able to give specifics on the size of the IS forces.
"On the radio we hear (IS) calling for reinforcements from Syria," Rebwar Gharib, a deputy sergeant on the central front line said Thursday.
The Islamic State group inflicted a wave of terror in the Sinjar area against the minority Yazidi community, members of an ancient religion whom the Islamic State group views as heretics and accuses of worshipping the devil. An untold number were killed in the August 2014 assault, and hundreds of men and women were kidnapped - the women enslaved and given to militants across the group's territory in Iraq and Syria, many of the men believed killed, others forced to convert.
Tens of thousands of Yazidis fled into the mountains, where the militants surrounded them, leaving them trapped and exposed in the blazing heat. The crisis prompted the U.S. to launch air drops of aid to the stranded, and then on August 8, it launched the first round of airstrikes in what would mark the beginning of a broader coalition effort to battle the militant group in Iraq and Syria.
Some of those stranded on Mount Sinjar were rescued by Syrian Kurdish fighters, who cleared a path for the Yazidis to descend from the mountain, cross into Syria, then cross back into northern Iraq's Kurdish autonomous zone. Then, in December, Kurdish fighters in northwestern Iraq managed to drive the militants out of areas on the other side of the mountain, opening a corridor that helped many of the remaining Sinjaris to escape. Those Kurdish fighters then tried to advance into Sinjar town itself but were fought off by the militants.
Various Kurdish militias on the town's edge have been fighting guerrilla battles for months with IS, damaging or destroying much of the picturesque town of ancient, narrow streets lined with modest stone homes. The factions include the Turkey-based Kurdish Workers' Party (PKK), the Syria-based People's Protection Units (YPG) and Yazidi-led forces billing themselves as the Sinjar Resistance. Iraqi Kurdish fighters have also held positions further outside the town.