The retake of Sinjar from the Islamic State (ISIS) is just a minor achievement and fighters should not be complacent as the terror group could just have pulled back or could be bidding their time before striking back, US and Kurdish officials warned.

The Kurdish flag has been raised and celebratory gunfire fired off in the centre of the town on Friday following a major offensive launched by Kurdish militias known as Peshmerga to recapture the strategic community, according to Fox News.

Peshmerga Maj. Ghazi Ali, who oversaw one of the units involved in the offensive, said thousands of Kurdish fighters entered the town from three directions Friday morning. Associated Press journalists have seen them raise a flag over a building in the centre of the city, said the report.

Ali said the Kurdish troops encountered minimal resistance during Friday's push but described the situation in the city as still "dangerous." Military leaders warned that it's too soon to declare victory.

Col. Steven Warren, a spokesman for the U.S.-led coalition also said it's too early to tell as the Kurdish fighters had not fully retaken Sinjar, said Fox News.

He confirmed that only Peshmerga fighters raised their flag on grain silos in the eastern part of the town.

On Thursday, Kurdish militia fighters reportedly succeeded in cutting a key highway nearby with U.S.-led coalition airstrikes supporting the offensive, dubbed Operation Free Sinjar.

Early Friday morning, hundreds of pickup trucks and sport-utility vehicles carrying Kurdish fighters were seen gathering at the entrance of Sinjar, ahead of a planned push into the town centre.

The skies above Sinjar were quiet overnight with little movement inside the city before Kurdish forces had moved in, said Diar Namo, the 26-year-old deputy commander of the Peshmerga unit stationed there,

"We saw more than 50 Daesh (ISIS fighters) flee overnight," Namo said. "Before there were only 200 to 300 in the city."

There were between 400 and 550 ISIS fighters inside Sinjar before the offensive began Thursday, according to estimates by the U.S.-led coalition.

Meanwhile in the village of Soulag, southeast of Sinjar, four Peshmerga fighters were killed when a homemade bomb targeting their truck exploded, according to fighters in their unit, said Reuters.

Homemade roadside bombs and explosives-laden cars targeting Peshmerga convoys have significantly slowed Thursday's advance through Sinjar's eastern and western fringe, it said.

The ISIS captured Sinjar on Aug. 3, 2014 during an offensive. Since then, thousands of people in the minority Yazidi communty have been displaced; thousands more killed, and its women, including young girls, enslaved, brutally tortured and raped.

According to reports, the Yazidis follow an ancient faith that the ISIS considers heretical.

Iraq's highest leader, Ayatollah Ali al-Sistani, commended the troops in his Friday sermon for their efforts to recapture the community from the Sunni militant group.