More than 5,000 people are now believed to have been killed in the Syrian government's crackdown on protests, UN rights chief Navi Pillay told the UN Security Council on Monday.
More than 14,000 people are estimated to have been detained and 12,400 have fled into neighboring countries, Pillay told a closed session of the 15-nation council, according to diplomats.
With hundreds more killed in December in President Bashar al-Assad's crackdown, "it is my estimation that the total number of people killed since the protests began earlier this year is now likely to exceed 5,000. This situation is intolerable," she was quoted as saying.
The Security Council held a private briefing on Syria and the rest of the Middle East with western nations stepping up pressure for the body to condemn the violence that erupted in March.
Russia and China vetoed a resolution on the Syria crisis in October.
After meeting with Pillay, German foreign minister Guido Westerwelle told reporters: "I think it is necessary that those countries in the Security Council which are still hesitating change their mind. I am really shocked about what I heard about the atrocities in Syria."
Westerwelle said the international community must now find "a common language" for the Security Council to "condemn these atrocities."
"We owe this to those who lost their lives," he said.
Among the council members, Russia, China, India, South Africa, and Brazil opposed or had strong reservations about any formal resolution which they said could be a first step to a western campaign for regime change.