More airstrikes and artillery shelling on Monday hit the northern Syrian city of Raqqa, the de facto capital of the Islamic State group, as US-backed fighters pushed closer to the extremists' stronghold, activists said.
The developments come ahead of what is expected to be a major battle for Raqqa in the coming weeks.
Airstrikes have intensified over the past days as US-backed fighters have pushed on toward the city, getting closer to it from all sides.
The Kurdish-led Syria Democratic Forces captured dozens of towns and villages under the cover of airstrikes by the US-led coalition since November, when the group began an operation entitled Euphrates Wrath, aiming to eventually surround and capture Raqqa.
SDF fighters have surrounded Raqqa from the north, west and east.
The extremists still have an exit from the south, even though the US-led coalition destroyed two bridges on the Euphrates River south of Raqqa.
The Britain-based Syrian Observatory for Human Rights said the city was pounded by warplanes and artillery since early morning.
The activist group had no immediate word on casualties from the new airstrikes, adding that about 38 people have been killed in Raqqa and its suburbs over the past three days.
The activist-operated Raqqa Is Being Slaughtered Silently said that since Sunday, the US-led coalition carried out more than 30 airstrikes on the city, killing 35 people and destroying a school on Raqqa's northern outskirts.
On Sunday, opposition activists said the US-led coalition dropped leaflets in Arabic on Raqqa, urging residents to leave the city.
Some leaflets gave instructions of how to leave Raqqa, calling on people to keep their plans secret from IS and to leave without any weapons and waving a white banner.
"This is your last chance. Failing to leave could lead to death. Raqqa will fall. Don't be there when it happens," read one of the leaflets.
IS has been preventing people from leaving Raqqa and many fear that residents will be used as human shields when SDF, the most effective force fighting the extremists in Syria, begin marching in the city that has been held by IS since January 2014.
In the capital, Damascus, preparations were under way for the last group of opposition fighters and their families to start leaving the northeastern neighbourhood of Barzeh.
The Observatory said those who will leave later on Monday are the ones who rejected an amnesty from the government.
Anas a-Dimashqi, an opposition activist based near Damascus, said the fighters and their families will head to the town of Jarablous on the border with Turkey and the rebel-held northwestern province of Idlib.
He said those who stay have up to six months to settle their conditions with the government.
Once Barzeh is emptied out of opposition fighters, President Bashar Assad's forces will be in full control of the capital for the first time in more than five years.