TEHRAN, Young Journalists Club (YJC) - "The intense bombardment of Raqqah over the past three weeks has reportedly left civilians terrified and confused about where they can seek refuge," Zeid Ra'ad al-Hussein said in a statement on Wednesday.
He warned that "up to 100,000 civilians are effectively trapped as the air and ground offensive intensifies."
US-backed Kurdish militants in Syria have been advancing toward Raqqah with heavy support from US-led airstrikes since November.
The UN rights chief said at least 173 civilians lost their lives in air and ground operations against Daesh this month in Raqqah, calling it a conservative figure.
He called on all sides involved in the fight against Daesh, "including international forces", to take all feasible precautions to spare the lives of the civilians who are still trapped in the province.
"Civilians must not be sacrificed for the sake of rapid military victories," Zeid added.
The US-led coalition has been conducting airstrikes against what are said to be Daesh targets inside Syria since September 2014 without any authorization from the Damascus government or a UN mandate.
The military alliance has repeatedly been accused of targeting and killing civilians. It has also been largely incapable of fulfilling its declared aim of destroying Daesh.
Syria has been fighting different foreign-sponsored militant and terrorist groups since March 2011.