China said on Thursday that it welcomes the Syrian government's agreement to a comprehensive cease-fire and troop withdrawal from some cities, marking important progress in the mediation efforts of UN-Arab League joint special envoy Kofi Annan.

Syrian forces halted attacks on opposition strongholds on Thursday, in line with a UN-brokered truce to end 13 months of bloodshed in Syria, despite skepticism that the cease-fire would hold.

"This will help ease the tense situation in Syria, and is an important step toward a political solution of the Syrian issue," Foreign Ministry spokesman Liu Weimin told a news conference.

"We hope the Syrian government will fully implement its commitment, continue to support and coordinate with Annan's efforts by means of concrete actions, and maintain the process of a political solution for the issue," Liu said.

He also urged armed Syrian opposition groups to stop fighting immediately and implement Annan's six-point plan.

Syrian rebels are fully committed to a UN-backed ceasefire which came into effect on Thursday, its spokesman said.

The onus is on Syria's government to keep to its promise to observe the cease-fire, UN Secretary General Ban Ki-moon told a news conference in Geneva on Thursday.

The situation in Syria looked calmer and he was working with the UN Security Council to send a team of truce observers as quickly as possible, once there is a mandate from world powers.

But he warned that the international community must remain unified to avoid Syria descending into chaos.

Annan's plan set April 10 as the deadline for troop withdrawal and April 12 as the deadline for a complete cease-fire between the Syrian army and opposition groups.

Annan said on Thursday that a cease-fire in Syria appears to be holding but Syrian President Bashar al-Assad must carry out all parts of an agreed peace plan.

"Syria is apparently experiencing a rare moment of calm on the ground," Annan said in a statement released as he briefed the UN Security Council.

The final cease-fire can hardly be achieved overnight, but needs all concerned parties' continuing efforts, said Li Huaxin, Chinese special envoy and former ambassador to Syria.

After the fighting stops, the next step would be to send observers to monitor the cease-fire, he added.

Russian Foreign Minister Sergei Lavrov called for more time on Thursday for Annan's peace plan to work and said Assad "is assuring us that he is ready" to comply with the six-point peace initiative.

US President Barack Obama and German Chancellor Angela Merkel agreed in a telephone call that the Security Council, which gave its blessing to Annan's plan, needed to "take more resolute action" on Syria.

According to Liu, China has been negotiating with the Syrian government and all relevant parties to ease the situation and promote a solution through political means.

"We are keeping up communication with Annan and fully support his mediation efforts," Liu said, adding that Foreign Minister Yang Jiechi also wrote to his Syrian counterpart, Walid Mualem, and welcomed the decision to halt military action and withdraw troops.

Xinhua and AFP contributed to this story.

zhaoshengnan@chinadaily.com.cn