International envoy Kofi Annan has just won backing from Russia for his Syrian mediation efforts but still faces tough questions from China, which opposes interference in the restive nation.

Annan, the UN-Arab League envoy on Syria, is due in Beijing on Tuesday to brief leaders about his proposal to end violence in the country, after visiting Russia, where President Dmitry Medvedev offered him Moscow's backing.

China and Russia have previously drawn criticism for blocking UN Security Council resolutions condemning Syria's protracted and deadly crackdown on protests, and their support is crucial for Annan's plan to move forward.

On Monday, China said it supported Annan's efforts to help solve the crisis and urged a peaceful solution but it was unclear whether this meant full support for Annan's plan or broad backing for his attempts.

"China values and supports the mediation efforts of Mr. Annan and hopes this visit will allow in-depth discussions on a political resolution of the Syrian issue," foreign ministry spokesman Hong Lei said.

Annan's proposal calls for a UN-supervised halt to fighting in Syria, with President Bashar al-Assad's government pulling its troops out of protest cities, and aims to push for a Syrian-led transition to a democratic system.

"Annan will probably gain a better understanding of how supportive the Chinese are (for his plan)," said Joshua Eisenman, senior fellow in China studies at the Washington-based American Foreign Policy Council.

"He'll get a sense of what the Chinese will bear and won't bear," he told AFP.

Analysts say that with Russia now firmly on board -- and Medvedev warning that Annan's plan represents the "last chance" for avoiding a civil war in Syria -- China faces more impetus to contribute to a solution.

"Since the Russians said yes first, it makes his (Annan's) job easier," said Eisenman.

But he said Beijing would still need persuading that there will be no foreign military intervention or attempt at regime change -- after Western efforts helped to depose Libyan leader Moamer Kadhafi.

"China of course hopes the (Syrian) government and opposition parties can reach consensus through negotiations," Jia Qingguo, professor of international relations at Peking University, said.

Summarising China's position, he said: "No country, including the United Nations, has a right to change the government of another country. This could have grave consequences."

As such, analysts say Beijing will be looking carefully at Annan's plans for a Syrian-led democratic transition.

"The issue is sovereignty. China doesn't support interference in the internal affairs of others," Eisenman said.

"China also has an authoritarian government. It fears Western pressure on its own political system and criticism of how it responds to dissent."

Beijing has uneasily watched developments in the Arab world -- where pro-democracy protests have in some countries toppled governments -- and has responded by cracking down on any hint of demonstrations at home.

But analysts say China has a strong interest in maintaining stability in the Middle East as the price of oil has already reached near record levels, posing a threat to its fast-expanding economic machine.

It has repeatedly called for an end to violence in Syria, and earlier this month it backed a UN statement urging Assad to work toward ceasing hostilities.

It has also unveiled its own six-point plan, calling for an immediate end to the conflict -- which monitors say has left more than 9,000 dead since March 2011 -- and for dialogue between Assad's regime and the opposition.