At least 79 people were killed on Wednesday in the central city, which sits adjacent to a UNESCO World Heritage Site, according to the Syrian Observatory for Human Rights.

"Once again Israeli airstrikes on Syria have increased significantly, both in frequency and scope," Najat Rochdi, UN deputy special envoy to Syria, told the Security Council.

"Just yesterday, we saw dozens killed in a strike near Palmyra -- likely the deadliest Israeli strike in Syria to date," Rochdi said.

She added that violence remains at "troubling levels" in other areas, including northwest Syria, where she cited an uptick in pro-government drone and artillery attacks.

Since the Syrian civil war erupted in 2011, Israel has carried out hundreds of strikes in the country. It has more recently intensified its strikes since almost a year of cross-border hostilities with Hezbollah in neighbouring Lebanon escalated into an all-out war in late September.

"Clearly, the immediate priority for Syria is de-escalation," Rochdi said. "As humanitarian aid diminishes and hostile rhetoric and actions intensify, Syrians are being driven into increasingly precarious and unsustainable conditions."

*This story was edited by Ahram Online.