BEIRUT: The civilian death toll in air strikes thought to have been conducted by a US-led coalition on a jihadist-held Syrian village on Thursday has risen to 23, a monitor said.
The Islamic State group is facing simultaneous offensives in northern Syria by government forces, Turkish-backed rebels, and a US-supported alliance of Kurdish and Arab fighters.
They are also being pummelled by Iraqi forces over the border in their most populous bastion Mosul.
"The raids hit the village of Al-Matab after midnight and were likely carried out by the coalition," said Rami Abdel Rahman of the Syrian Observatory for Human Rights.
The Observatory earlier reported 14 people killed.
At least eight children and six women were among the dead in Al-Matab, which is held by the Islamic State group.
The village lies near a key road linking IS's de facto Syria capital Raqa with the partly-IS held city of Deir Ezzor further down the Euphrates Valley.
On Monday, fighters of the US-backed Syrian Democratic Forces cut off the road in a bid to encircle the jihadists in Raqa.
The US-led coalition has been backing the SDF's drive on the IS stronghold with air power and hundreds of military advisers.
Abdel Rahman said SDF fighters were advancing on Al-Matab, which lies about 55 kilometres (35 miles) southeast of Raqa.
The SDF launched its drive on the city in early November and has since seized swathes of territory.
But it is despised by Ankara, which condemns the group's dominant component -- the Kurdish People's Protection Units (YPG) -- as "terrorists" because of its links to an outlawed Kurdish rebel group in Turkey.
The profusion of forces operating in Syria -- particularly in its fractured north -- has led to a deeply complex battlefield and tensions between the rival parties.
The US-led coalition fighting IS said earlier this month that its raids in Iraq and Syria had unintentionally killed at least 220 civilians since 2014.
Critics say the real number is much higher.
Further east, in Deir Ezzor province, suspected Russian strikes hit the IS-held town of Al-Mayadeen, killing seven civilians and wounding 70, the Observatory said.
"The dead included three children and their parents," said Abdel Rahman.
Al-Mayadeen lies on the Euphrates River between Deir Ezzor and the Iraqi border.
The Observatory, which relies on a network of sources inside Syria for its information, says it determines whose planes carry out raids according to type, location, flight patterns and munitions used.
More than 310,000 people have been killed since conflict broke out in Syria in March 2011 with protests against the rule of President Bashar al-Assad.