The toll in air strikes thought to have been conducted by a US-led coalition on a jihadist-held northern Syrian village on Thursday has risen to 23 civilians killed, a monitor said.
"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 a toll of 14 people killed.
At least eight children and six women were among the dead in Al-Matab, held by the Islamic State group.
The village lies near a key road linking Raqa -- IS's de facto capital -- to Deir Ezzor city, the capital of the adjacent oil-rich province.
On Monday, fighters from the US-backed Syrian Democratic Forces cut off that route in a bid to encircle the jihadists in Raqa.
The US-led coalition has been backing the SDF's drive for Raqa with air power and hundreds of special operations forces as advisers.
Abdel Rahman said SDF fighters advancing on IS jihadists in Al-Matab, which lies about 55 kilometres (35 miles) southeast of Raqa.
The SDF, an alliance of Kurdish and Arab fighters, launched its offensive for Raqa in early November and has since seized swathes of territory in northern Syria.
But it is despised by Ankara, who condemns the group's dominant component -- the Kurdish People's Protection Units (YPG) -- as "terrorists" because of its links to an outlawed Kurdish militia in Turkey.
The profusion of forces operating in Syria -- particularly in its fractured north -- has led to a deeply complex battlefield and tensions between different parties.
The US-led coalition fighting IS in Syria and Iraq said earlier this month that its raids had unintentionally killed at least 220 civilians since 2014 in both countries.
Critics say the real number is much higher.
More than 310,000 people have been killed since Syria's conflict erupted in March 2011 with protests against the rule of President Bashar al-Assad.