US-led coalition air strikes have killed dozens of civilians in the Syrian city of Raqqa over the past 24 hours, activists and state media say.
The Syrian Observatory for Human Rights reported that 42 had died in attacks on areas held by so-called Islamic State.
Anti-IS group Raqqa is Being Slaughtered Silently said 32 were killed in one district alone.
The coalition said it adhered to strict targeting processes and procedures aimed to minimise risks to civilians.
Its aircraft are supporting a ground assault on Raqqa by the Syrian Democratic Forces (SDF) alliance, which is believed to have captured more than than half of the de facto capital of the IS "caliphate" since early June.
The Syrian Observatory, a UK-based group that monitors the six-year-old civil war through a network of sources, said on Tuesday that 19 children and 12 women were among those killed in Monday's air raids on the Sukhani and Badu districts.
The figures took to 167 the number of civilians killed in coalition strikes since 14 August, it said.
"The tolls are high because the air strikes are hitting neighbourhoods in the city centre that are densely packed with civilians," Syrian Observatory director Rami Abdul Rahman told AFP news agency.
Hussam Essa of Raqqa is Being Slaughtered Silently said: "Unfortunately, civilians have no way to protect themselves. All they can do is try to hide in whatever shelter they can and avoid going out into the street as much as possible."
The coalition said it took all allegations of civilian casualties seriously and assessed those deemed credible, but that those made by the Syrian Observatory in recent days lacked "specificity and detail making it very difficult to properly assess".
"The coalition respects human life and our goal is always for zero civilian casualties," it added. "Coalition forces take all reasonable precautions during the planning and execution of airstrikes to reduce the risk of harm to civilians."
Earlier, it said coalition warplanes had conducted 20 air strikes in the Raqqa area on Monday, engaging 13 IS tactical units and destroying 24 fighting positions, a vehicle, a logistics node and communications infrastructure.
At the start of June, the coalition said its 22,983 air strikes in Syria and Iraq since 2014 had unintentionally killed at least 624 civilians. However, human rights groups believe the true figure is far higher.
Airwars, an organisation that tracks allegations of civilian deaths, said that as of 8 August, coalition air strikes were likely to have killed at least 4,487 civilians.
On Monday, UN spokesman Stéphane Dujarric told reporters that it was deeply concerned for the safety of up to 25,000 civilians trapped inside Raqqa, many of them women and children.
Tens of thousands of people had fled the city, but those remaining faced severe restrictions of movement in and out of the city, which had dwindling food and water supplies, he said.
"The UN stresses again that all parties to the fighting are obligated to protect civilians under international humanitarian law, as well as the need for sustained and unhindered access to those who need help," Mr Dujarric added.