China on Wednesday defended the Arab League's widely criticised observer mission to Syria as Russia warned against imposing sanctions on the regime of President Bashar al-Assad.

Syria's state-run media accused the Gulf state of Qatar of fuelling the crisis by financing and arming rebels fighting the security forces after Damascus flatly rejected Doha's proposal to send in Arab troops.

"Since the Arab League observer mission began, the violence in Syria has not completely ended, but the security situation of major areas has improved," said Chinese foreign ministry spokesman Liu Weimin.

"(This) shows the mission is effective," he added.

Russia, which insists the Syrian opposition is as much to blame for the violence as the regime, warned against Western calls for punitive measures against Damascus.

"For us, the red line is fairly clearly drawn. We will not support any sanctions," said Foreign Minister Sergei Lavrov, whose country was a Cold War ally of Damascus and retains a naval base at Tartus on Syria's Mediterranean coast.

Despite the opposition from Moscow, European Union foreign ministers are set to tighten the bloc's unilateral sanctions against Damascus next week, diplomats said.

Eight companies and 22 individuals will be added to an existing EU blacklist, the diplomats said.

"As long as the repression continues, we will step up our restrictive measures," one diplomat said, speaking on condition of anonymity.

Syria's state-owned media stepped up its rhetoric against Qatar ahead of a meeting of ther Arab League on Saturday and Sunday which will discuss its proposal for Arab troops as well as the future of the observer mission.

The Gulf state "can help Syria get out of its crisis... by stopping its financing of armed (groups) and the trafficking of weapons" to insurgents, the government newspaper Tishrin charged.

Damascus routinely blames the violence in Syria on "armed groups" and "terrorists" backed by foreign powers pursuing an agenda of regime change.

On Tuesday, the Syrian foreign ministry dismissed the Qatari call for Arab troops to be deployed to halt the bloodshed, which the United Nations says has cost more than 5,400 lives since March.

"Syria rejects the statements of officials of Qatar on sending Arab troops to worsen the crisis ... and pave the way for foreign intervention," a ministry statement said.

In an interview with US television network CBS aired at the weekend, Qatar's emir, Sheikh Hamad bin Khalifa Al-Thani, said he favoured sending Arab troops to Syria to "stop the killing."

From its base in Turkey, the rebel Free Syrian Army called on the Arab League to "quickly transfer the case of Syria to the UN Security Council," in a statement signed by its leader Riyadh al-Asaad, a dissident colonel.

The United Nations pledged this week to assist the Arab mission deployed in Syria since last month, saying it would start training the bloc's observers within days.

But the rebels, who claim to have more than 40,000 men in their ranks, demanded bolder action from the world body, urging it to "act quickly against the regime through Chapter Seven of the UN Charter to maintain peace."

Chapter Seven provides for UN forces to initiate military action, not simply act in self-defence.

Diplomats at the United Nations said experts from the 15 members of the Security Council held prolonged talks Tuesday on a proposed Russian resolution on Syria without getting closer to UN action on the bloodshed.

"There were more than four hours of talks but they only touched on the preparatory paragraphs," one Western diplomat said.

"We don't feel a real effort to close the gaps," commented another Western diplomat.

Western governments oppose the Russia text which they say wrongly equates security force violence with what they say is far less frequent armed action by the opposition.

After White House talks with King Abdullah II of Jordan on Tuesday, US President Barack Obama described the regime's crackdown as "unacceptable" and vowed to redouble efforts to secure a change of government.

"We will continue to consult very closely with Jordan to create the kind of international pressure and environment that encourage the current Syrian regime to step aside so that a more democratic process and transition can take place inside of Syria," he said.

In violence on Tuesday, at least 20 civilians were killed, eight of them when a blast hit a minibus in Idlib province in the northwest, the Syrian Observatory for Human Rights said.

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