The US-led coalition confirms that it has carried out airstrikes in the Syrian province of Deir ez-Zor but refutes media reports about mass civilian casualties caused by the strikes, coalition's spokesman Col. Sean Ryan told Sputnik on Saturday.
Syria's official SANA news agency confirmed that the army units had made "a significant advance against Daesh terrorists' depots in Tulul al-Safa" and killed many extremists during their counter-terrorism operations.
The US-backed Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab fighters led by the YPG Kurdish militia, has been fighting on the ground since September to expel IS fighters from a pocket around Abu Husn.
The US-led coalition, however, continued with airstrikes against IS.
The Observatory said coalition air strikes early Saturday on the village of Abu al-Husn in Deir Ezzor province killed 43 people, including 36 family members of IS fighters. He said it was not immediately clear if the men killed in the strikes were militants.
Abou Diab says the Islamic State pocket in the region of Deir el-Zour is one of several he says are supported by different countries involved in the Syria conflict.
The SOHR has recorded at least 191 civilian deaths since 10 September. They are mostly Iraqis and believed to include family members of ISIS militants, the organization added.
He says that the final pockets of Islamic State fighters have taken advantage of poor weather conditions (and cloud cover) to capture positions and equipment belonging to the US coalition, prompting fierce fighting in an effort to recapture lost ground.
IS overran large swathes of Syria and neighboring Iraq in 2014, proclaiming a "caliphate" in land it controlled.
In Syria, the group has seen its presence reduced to parts of the vast Badia desert and the pocket in Deir Ezzor.
Following the setback, hundreds of Kurdish fighters were deployed to the area's outskirts as reinforcements.
The SDF assault was slowed by a fierce militant fightback, and then briefly put on hold to protest Turkish shelling of Kurdish militia positions in northern Syria.
On Sunday, the SDF said it was resuming its offensive against IS after "intensive contacts" with the coalition and "strong diplomatic activity" to defuse the crisis.
The coalition has since 2014 acknowledged direct responsibility for over 1,100 civilian deaths in Syria and Iraq, but rights groups put the number killed much higher.
Syria's war has killed more than 360,000 people since it erupted in 2011 with the repression of anti-government protests.