The UN High Commissioner for Human Rights has said that both sides in the Syrian conflict were to blame for human rights abuses.
Addressing the 47-member UN Human Rights Council in Geneva, Navi Pillay reiterated that the Syrian government's actions might amount to war crimes and crimes against humanity.
"The use of heavy weapons by the government and the shelling of populated areas have resulted in high numbers of civilian casualties, mass displacement of civilians inside and outside the country and a devastating humanitarian crisis," she said.
"I am equally concerned about violations by anti-government forces, including murder, extrajudicial execution and torture, as well as the recently increased use of improvised explosive devices."
Ms Pillay has repeatedly called for Syria to be referred to the International Criminal Court, but such a referral can only be effected by the UN Security Council, which is split on how to deal with Syria.
China and Russia oppose any attempt to lay the blame for the crisis on President Bashar al-Assad.
The Human Rights Council has repeatedly voted to condemn Syria's government for its handling of what began as a peaceful protest movement against the government and has escalated into civil war.
China, Russia and Cuba have consistently voted against its resolutions.
The Syrian Observatory for Human Rights, an opposition watchdog based in London, says more than 23,000 people have died in the uprising that has lasted more than 17 months.
About 200,000 Syrians have fled to Turkey, Jordan, Iraq and Lebanon.
UN Secretary-General Ban Ki-moon said he regretted that the Human Rights Council's recommendations had not been followed up by other UN bodies, and urged the council to keep up its vigilance on Syria, "including on the question of accountability".
"We must ensure that anyone, on any side, who commits war crimes, crimes against humanity or other violations international human rights or humanitarian law is brought to justice," he told the meeting.