Army presses advance on militants at Syria's biggest dam
Government troops and militia advanced on Syria's largest dam with Russian air support on Monday, threatening to cut off the militants' bastion Raqqa from the Turkish border.
The advance took the army to within 24 kilometres (15 miles) of Lake Assad, the vast reservoir in the Euphrates Valley contained by the Tabqa dam, the Syrian Observatory for Human Rights said.
The militants are being caught in a pincer movement by Russian-backed government forces advancing on Tabqa from the southwest and US-backed Kurdish and Arab fighters advancing on the dam from the north.
The coincidence of the twin offensives has raised speculation about possible covert coordination between the two governments on their operations in Syria.
Washington's allies in the Syrian Democratic Force (SDF) have also attacked IS farther north, crossing the Euphrates near the Turkish border and nearing the militant-held city of Manbij.
Manbij lies at the heart of a pocket of IS-held territory along the border that US commanders regard as the principal entry point for foreign fighters and funds.
Washington has deployed more than 200 special forces troops with the SDF to oversee the offensive.
The SDF has captured more than 40 villages from IS since it launched the operation last week. It has lost 19 fighters while the militants have lost 56, according to the Britain-based Observatory.
The Syrian government has lost nine troops and militiamen in its advance, which has killed at least 70 IS fighters since Saturday.
Yazidi captives freed
In the village of Halula just east of Manbij, an AFP reporter saw several US soldiers in jeeps as they assisted SDF fighters, as well as dozens of civilians who had fled areas around Manbij, including many children, most with few belongings.
"They lived near us and we had to do what they said or they would kill our children or take our homes," mother of nine Jawaher said of IS.
The United Nations says that at least 20,000 civilians have fled the fighting around Manbij.
At least 74 people have died in fighting since the offensive began last Monday, including 32 civilians mainly killed in coalition airstrikes, said the Observatory.
Thirty militants were also killed along with 12 SDF fighters, said the monitor which relies on sources on the ground for its reports.
After taking the village of Khirbet al-Rus, southeast of Manbij, the SDF rescued six women and 16 children, all of them Yazidis who were being held captive by IS, it added.
IS abducted hundreds of Yazidis in mid-2014 as it carried out a brutal campaign of massacres, enslavement and rape against the minority.
Since starting with a 2011 crackdown on anti-government protests, Syria's conflict has evolved into a complex, multi-front civil war that has left more than 280,000 dead and forced millions from their homes.
The Islamic State group emerged from the chaos of the war in mid-2014, seizing control of large parts of Syria and neighbouring Iraq, declaring a fundamentalist Islamic "caliphate" and committing widespread atrocities.
Diplomatic efforts to get Syria's regime and non-militant rebels to move towards peace have been thwarted by a lack of trust and continued fighting, especially around the second city Aleppo, which is divided between government and rebel control.