US-backed Syrian fighters have clashed with Islamic State militants in the heart of Raqqa, the extremists' self-styled capital, as scores of civilians flee areas controlled by the group.
The Syrian Democratic Forces (SDF), aided by the US-led coalition, launched their offensive to capture the city on June 6, and have since taken several areas.
The Britain-based Syrian Observatory for Human Rights said the fighting is concentrated in the south-western neighbourhood of Yarmouk and the Old City.
The SDF said intense fighting is under way in central Raqqa, adding that its fighters have taken positions near a centuries-old mosque.
The Kurdish-run Hawar news agency said some 180 civilians were able to flee areas controlled by IS while the Observatory put the number in the hundreds.
The SDF said 11 IS fighters have been killed in the clashes since Sunday.
The IS-linked Aamaq news agency said 14 SDF fighters were killed in the fighting in Raqqa on Sunday alone.
The intensification of fighting comes a week after Iraqi forces declared victory against IS in the northern Iraqi city of Mosul, the largest the extremists have held.
The loss of Raqqa would deal a major blow to IS, but the group still holds wide areas of the eastern province of Deir el-Zour, bordering Iraq.