China's foreign minister on Tuesday urged all parties in Syria to honour their ceasefire commitments, as the United Nations warned world powers were racing against time to stop war in the restive state.

Speaking to Burhan Ghalioun, the visiting head of the opposition Syrian National Council (SNC), Yang Jiechi also urged the government and opposition groups to cooperate with a UN mission deployed in the country.

China has traditionally backed Syrian President Bashar al-Assad, and it drew international criticism earlier this year for vetoing two UN Security Council resolutions on the crisis, along with Russia.

But it has also backed UN-Arab League envoy Kofi Annan's efforts to bring peace to Syria in the form of a six-point proposal agreed by Damascus that includes a ceasefire and withdrawal of troops.

"All parties in Syria must abide by their ceasefire commitments, support and cooperate with the work of the UN supervision team, to create the conditions to launch an inclusive political process as soon as possible," Yang told Ghalioun.

His comments -- published on the foreign ministry website -- came as UN leader Ban Ki-moon condemned the "brutality" of Assad's forces but said attacks by opposition groups had also "escalated".

"We are in a race against time to prevent full-scale civil war -- death on a potentially massive scale," Ban said ahead of a key UN Security Council meeting on Syria.

The UN already estimates that more than 9,000 people have died in the 14-month uprising against Assad, while rights groups have put the number beyond 11,000.

Ghalioun arrived in China on Sunday and is due to leave on Wednesday.

The Syrian government on Monday held parliamentary elections while violence still raged, but the polls were dismissed as a sham by the main opposition forces, which have refused to participate.

Neither Yang nor Ghalioun mentioned the elections in the short statement, but the SNC leader told Yang the council "advocates a political solution to the Syrian crisis and supports Annan's six-point proposal".