"We believe, and we've said it and we'll keep repeating it, that the case of Syria belongs in the International Criminal Court. This would give a very, very strong message to those running the show," Rupert Colville, spokesperson for UN High Commissioner for Human Rights Navi Pillay, told a news briefing.
Pillay will address a UN General Assembly session on Syria being held in New York on Monday, Colville said. "I believe they are considering a resolution, what it will contain I don't know," he added.
Pillay, a former UN war crimes judge, called on Wednesday for urgent international action to protect civilians in Syria, saying she was appalled by the Syrian government's military onslaught on the city of Homs.
Twin bomb blasts hit military and security buildings in the northern city of Aleppo on Friday, killing 25 people in the worst violence to hit Syria's commercial hub in the 11-month uprising against President Bashar Assad.
The UN has stopped issuing a death toll for Syria, saying the widespread violence made it impossible to cross-check reports and provide a reliable figure. More than 5 000 people had been killed as of December 12, according to its last estimate.
"Clearly the numbers are climbing every day, and it's really a pretty disastrous situation in Homs. But we can't give you even a ballpark figure and endorse it," Colville said.
Increase in war wounded
Asked who should refer Syrian figures to the Hague-based ICC for prosecution, Colville replied: "As things stand only the Security Council can do that."
Russia and China provoked strong condemnation from the United States, European powers and Arab governments when they vetoed a resolution in the Security Council last week that called on Assad to step down.
The World Health Organisation (WHO) said on Friday there had been a "massive increase" in the number of war wounded in Syria, though its Damascus office could provide no figures.
"There is also a disruption of regular health services due to lack of security, limited access, staff cannot reach health facilities and also sick or wounded people have difficulty reaching health facilities," WHO spokesperson Fadela Chaib said.
"We remind all parties that health workers and health premises should not be targeted in any way, they should be seen as neutral premises," she added.
A UN commission of inquiry on Syria, in a report issued last November, said that Syrian military and security forces had committed crimes against humanity, including murder, torture and rape of civilians.
An initial UN inquiry into the Syrian uprising issued a report in August with a confidential list of 50 suspects whom it said were linked to alleged crimes against humanity.