Syrian troops attacked rebel strongholds in Deraa on Wednesday where the uprising against President Bashar al-Assad erupted nearly a year ago, and the UN chief said crimes against humanity may have been committed in Syria.
The assault on Deraa followed a push against rebels in the cities of Hama and Homs, which has faced nearly two weeks of bombardment from Assad's forces, in an apparent drive to crush the 11-month-old uprising against his rule.
Assad has intensified a crackdown on protesters and insurgents, while also setting a February 26 referendum on a draft constitution that would end the Baath Party's monopoly on power, to be followed by a multi-party parliamentary election.
Syria's opposition and Western powers dismissed the promised reforms and UN secretary general Ban Ki-moon, speaking before a non-binding vote at the United Nations on a draft resolution aimed at increasing pressure on Assad, said potential crimes against humanity were being carried out in Syria.
"We see neighbourhoods shelled indiscriminately, hospitals used as torture centres, children as young as 10 years old abused and killed. We see almost ... certain crimes against humanity," he told reporters in Austria.
China, which along with Russia blocked a draft resolution at the UN Security Council backing an Arab call for Assad to step aside, said it was sending a senior envoy to Syria.
"(China) does not approve of the use of force to interfere in Syria or the forceful pushing of a so-called regime change," vice foreign minister Zhai Jun said.
Zhai, who will travel to Syria on Friday and Saturday, said China believed that "sanctions or the threat of sanctions are not conducive to the appropriate resolution of this issue".