A UN General Assembly committee strongly condemned human rights violations in Syria's nearly five-year war on Thursday and said perpetrators of war crimes should face trial.

A resolution presented by Saudi Arabia was adopted by a vote of 115 to 15, with 51 abstentions.

China, Iran and Russia were among the countries that voted against the measure that now goes to the full General Assembly.

The resolution expresses "outrage" at the worsening violence that has left at least 250,000 dead and displaced more than 12 million people.

It stressed the need for accountability and encouraged the UN Security Council to take action, noting that the International Criminal Court (ICC) could play a role.

An attempt last year to refer Syria to the ICC for war crimes was blocked by Russia, Syria's ally, and China at the Security Council.

Presenting the resolution, Saudi Ambassador Abdallah al-Mouallimi recalled images of three-year-old Alan Kurdi, a Syrian boy who drowned during his family's flight from the war.

"I appeal to you not to let Alan down. Do not kill him twice," said the Saudi ambassador to the assembly.

Syria's UN envoy responded by attacking Saudi Arabia, accusing Riyadh of financing Wahhabi extremists and failing to uphold human rights on its own territory.

"Can anyone consider the Saudi regime as a pluralistic, democratic system where women participate fully and effectively?" asked Bashar Jaafari.

He accused the Saudi regime of "decapitation and flogging in public squares, (and of) religious persecution similar to what the terrorists of Daesh are doing in my country and Iraq."

The Islamic State (IS) group is sometimes referred to by the Arabic acronym Daesh.

The resolution condemned attacks committed by the IS group, but it deplored the "continued, widespread and systematic gross violations of human rights" by the Syrian authorities and its associated militias.

Last year the resolution was adopted by a stronger margin, with 125 countries voting in favour, 13 against and 47 abstentions.