United Nations, United States (AFP): UN Secretary-General Antonio Guterres said on Monday he was "alarmed" by the escalation of violence in Syria and called for an immediate end to fighting that his organization says has displaced nearly 50,000 people.

"All parties must do their utmost to protect civilians and civilian objects, including by allowing safe passage to civilians who are fleeing hostilities," Guterres's spokesman Stephane Dujarric said in a statement.

"Syrians have endured the conflict for nearly 14 years. They deserve a political horizon that will deliver a peaceful future, not more bloodshed," he added.

Syria has been at war since President Bashar al-Assad cracked down on pro-democracy protests in 2011, with subsequent fighting that has involved foreign powers and jihadists leaving an estimated half a million people dead.

The conflict had been mostly dormant, with Assad back in control of much of the country until last week, when a rebel alliance led by Islamist armed groups began its offensive.

Syria's military and its ally Russia have responded with deadly air raids on areas under rebel control.

The fighting has killed more than 457 people, including at least 72 civilians, according to the Syrian Observatory for Human Rights.

As of November 30, more than 48,500 people had been displaced in Idlib and northern Aleppo, more than half of them children, the UN's humanitarian agency OCHA said on Monday, adding that the situation was highly fluid.

"Tens of thousands of people on the move; critical services interrupted; women, men and children fearing for safety," OCHA chief Tom Fletcher said on X, describing the situation as "worrying."

"Syrians have already endured over 13 years of suffering. All sides must do more to protect civilians."

The number of displaced was a steep increase from the 14,000 people reported on 28 November.

And according to Dujarric, UN peacekeeping operations in the country have been "largely suspended" across Aleppo, Idlib and Hama due to security concerns.

"This has led to severe disruption in people's ability to access life-saving assistance," he said, adding that the United Nations remained committed to delivering humanitarian aid.

Dujarric warned that "the presence of unburied bodies and lack of drinking water" in Syria threatens public health and said that damage to Aleppo's university hospital had left hundreds of patients without care.

"Syria is also already one of the world's largest humanitarian crises, with 16.7 million human beings in need of assistance and over seven million people internally displaced," he said.

Israel's stepped-up offensive against Hezbollah in neighboring Lebanon since September had also had an effect on the situation, he said.

"More than half a million people have also fled from Lebanon to Syria in recent weeks, and winter conditions will only make the needs in the coming weeks even more acute."