SINJAR, Iraq -- Dealing a double blow to the Islamic State group, Iraqi Kurdish forces pushed into the key town of Sinjar on Friday as a Syrian rebel coalition captured an IS-held border town in northern Syria.

In Iraq, the Kurdish forces raised a Kurdish flag in the centre of Sinjar and a top official said it was liberated, though U.S. and Kurdish military officials urged caution in declaring victory in a major offensive to retake the strategic community.

The Kurdish forces encountered little resistance, at least initially, suggesting that many of the IS fighters may have pulled back in anticipation of Friday's advance. It was also possible that they could be biding their time before striking back.

Kurdish militia fighters known as peshmerga forces launched the offensive to retake Sinjar on Thursday, and succeeded in cutting a key nearby highway. U.S.-led coalition airstrikes supported the offensive, dubbed Operation Free Sinjar. The town has been under the control of the Islamic State group for more than a year.

Meanwhile, across the border in Syria, a coalition of Arab, Christian and Kurdish rebel factions known as the Democratic Forces of Syria seized the town of Hol in northern Hassakeh province. The U.S.-backed offensive to retake IS-held areas in the southern parts of Hassakeh is coinciding with the push to retake Sinjar.

Redur Khalil, the spokesman for the main Kurdish fighting faction in Syria known as the YPG, announced that the coalition took Hol.

The Britain-based Syrian Observatory for Human Rights also reported the Democratic Forces of Syria had reached Hol. It said the Syrian fighters on the ground were backed by intense air strikes by the U.S.-led coalition that killed dozens of IS militants. Others fled, leaving their weapons and ammunition behind.

It was the biggest victory for the Syrian coalition, which was formed in mid-October. The push to liberate southern Hassakeh province from IS was announced shortly after that.

A senior Kurdish defence official, Nasser Haj Mansour, told The Associated Press earlier that the fighters of the coalition had reached the outskirts of Hol. He said IS militants were burning houses as they fled the town while others were using the few civilians left in the area as human shields.

In Iraq, Sinjar has been under the control of the Islamic State group for more than a year. The town was overrun by the extremists as they rampaged across Iraq in August 2014, leading to the killing, enslavement and flight of thousands of people from the minority Yazidi community.

"We promised, we have liberated Sinjar," Massoud Barzani, the president of the semi-autonomous Kurdish region, told fighters in Sinjar. "It's time for the Yazidi girls to raise their heads up. Revenge has been taken for them."

"Sinjar is very important because it's become a symbol of injustice against the Kurdish people," he added.

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

They encountered minimal resistance during Friday's push, Ali said.

"No one was fighting back. They placed some IEDs and had some snipers in position, but there were no clashes," he said, using the abbreviation for improvised explosive devices, a military term for homemade roadside bombs.

Gunfire fell silent as peshmerga fighters marched into the town. He described the situation in the city as still dangerous, however, and warned that it was too soon to declare victory.

"I can't say the operation is complete because there are still threats remaining inside Sinjar," he said. The risks include ambushes from suicide bombers, roadside bombs and booby-trapped houses, he added.

Associated Press writers Vivian Salama, Qassim Abdul-Zahra, Zeina Karam and Murtada Faraj contributed to this report from Baghdad.