Beirut: The U.S.-backed Syrian Democratic Forces (SDF) said on Wednesday its campaign to capture Raqqa from IS was in its final stages and its fighters had seized 80 percent of the city.
The SDF said in a statement it had opened a new front against IS on the northern edge of Raqqa.
This was "a feature of the final stages of the Euphrates Wrath campaign, which is nearing its end".
The SDF, an alliance of Kurdish and Arab militias, launched its offensive on IS in Raqqa city in June, backed by U.S.-led air strikes and special forces on the ground.
The city had served as IS' de facto capital in Syria.
"We can say that 80 per cent of the city of Raqqa has been liberated," the statement said.
The Syrian Observatory for Human Rights said on Wednesday that the SDF had taken more than 90 per cent of the city, adding that the major remaining hurdle for the forces was a large concentration of mines in the area.
The remaining IS militants in the city have nearly run out of food and munitions, the Observatory reported.
IS is also battling two separate offensives in eastern Syria, launched by the SDF on one side and the Syrian army and its allies on the other in Deir Al Zor province.
The Syrian army, backed by Russian and Syrian war planes, has made wide advances along the Euphrates' western riverbank, the Observatory reported.
Syrian troops also crossed to the eastern side of the river on Monday.
The SDF's advances have been on the eastern bank of the river.
The convergence of the two rival offensives has increased tensions in Deir Al Zor.
The U.S.-backed militia on Monday warned against any further Syrian army advances on the eastern riverbank.
On Tuesday, Russia's Defence Ministry said the Euphrates had risen as soon as the Syrian army began crossing it.
The only way that could have happened was if upstream dams held by the U.S.-backed opposition had been opened, it said.
A fire at a major gas field known as Conoco raged through Tuesday night and into Wednesday, the Observatory said, after Syrian state media reported that the army was advancing towards it.
IS had fled the area, the Observatory said.
The hardline militants lost their main stronghold in Iraq, the city of Mosul, in July to Western-backed Iraqi forces.