More than 500 people have been killed in 2,000 air strikes across Syria by regime forces over the past 40 days, a monitoring group said Friday.
The Syrian Observatory for Human Rights accused President Bashar al-Assad's government of "war crimes", saying it ought to be "listed in the Guinness Book of World Records" for the large number of strikes since October 20.
The Britain-based group, which relies on a broad network of activists and medics on the ground for its information, said the raids had left at least 527 dead and 2,000 wounded.
The Observatory called on the international community "to take real steps towards putting an end to war crimes and crimes against humanity that the Syrian people are suffering daily, and for Syria to be referred to the International Criminal Court".
On Wednesday alone, raids on the Islamic State (IS) jihadist group's self-declared "capital" of Raqa killed 95 people, "the vast majority civilians", according to the Observatory.
The United States said it was "horrified" by the bloodshed in Raqa, where a US-led coalition has also targeted the IS with air raids.
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"The Assad regime's continued slaughter of Syrian civilians further exposes its callous disregard for human life," State Department spokeswoman Jen Psaki said.
The multi-sided Syrian conflict has killed more than 195,000 people since it began three and a half years ago as an uprising against Assad's regime.
The Syrian air force first launched air strikes against rebel-held areas in July 2012 when the government lost control of swathes of Aleppo city.
It has since pounded areas across the country on a daily basis, often with crude "barrel bombs" dropped from helicopters.
"In the past 40 days alone, there have been strikes against parts of 12 of Syria's 14 provinces," Observatory director Rami Abdel Rahman told AFP.
"Millions of people have fled their homes because of the strikes, becoming internally displaced or refugees in neighbouring countries," he said.
Syria's air force currently has 275 warplanes, having lost 87 aircraft last year, some shot down by rebels, according to the Washington-based Centre for Strategic and International Studies.
The United Nations and rights groups have repeatedly urged all sides in Syria's war to refrain from using weapons that fail to discriminate between military and civilian targets.