Fierce clashes on Sunday killed at least 22 Syrians, mostly soldiers, as opponents of President Bashar al-Assad sought to up the pressure for UN action after the Arab League withdrew its observers.

League chief Nabil al-Arabi, departing Cairo for the United Nations, said he hoped for a change of stance by Russia and China on a draft Security Council resolution that would back an Arab plan to end the Syrian crisis.

According to a tally taken from reports by the Syrian Observatory for Human Rights and state media, at least 232 people - among them 147 civilians - have been killed since Tuesday.

That adds to the figure of more than 5,400 given by the United Nations last month since anti-regime protests erupted in mid-March.

Arabi has said the decision to suspend the monitoring mission was taken 'because of the upsurge of violence whose victims are innocent civilians' and after Damascus 'chose the option of escalation'.

There was no sign of a let-up in the killing on Sunday, with activists and state media reporting the deaths of 16 soldiers in two separate attacks and five civilians and a deserter killed.

The Observatory reported 10 members of the military killed when their convoy was attacked in Jebel al-Zuwiya in the northwest, and the official SANA news agency said 'an armed terrorist group' killed six others near Damascus.

The Observatory also reported four civilians and a deserter killed as soldiers and mutineers clashed in the Ghuta area near the capital. It said another civilian was killed in Homs.

Moscow on Sunday expressed surprise at the Arab League decision to withdraw its monitors.

"We would like to know why they are treating such a useful instrument in this way," Foreign Minister Sergei Lavrov said during a visit to Brunei, cited by Russia's ITAR-TASS news agency.

"I would support an increased number of observers," he said.

"We are surprised that after a decision was taken on prolonging the observers' mission for another month, some countries, particularly Persian Gulf countries, recalled their observers from the mission."

The 165 observers deployed a month ago after Damascus agreed to the Arab League plan foreseeing a halt to the violence, prisoners freed, tanks withdrawn from built-up areas and free movement of observers and foreign media.

Arabi said on Sunday he hopes Moscow and Beijing will allow the UN Security Council to issue a resolution backing a League plan to end the crisis.

"I hope these two countries will alter their position concerning the draft UN Security Council resolution which would adopt the Arab plan," he said, according to Egypt's official MENA news agency.

The League plan looks to a halt in the violence and Assad transferring power to his deputy ahead of negotiations - a formula flatly rejected by Damascus.

Moscow opposes the draft UN resolution, and has proposed its own draft assigning equal blame for the violence on both Assad and the opposition, an option dismissed by the West.

The opposition Syrian National Council has called for protests outside Russian diplomatic missions, and SNC chief Burhan Ghaliun is also travelling to New York on Sunday 'to present the Syrian case... and demand protection'.

Lavrov said on Sunday he did not back those Western countries that said the monitoring mission was pointless and that it was impossible to hold dialogue with Assad's regime.

"I think these are very irresponsible statements because trying to sabotage a chance to calm the situation is absolutely unforgivable," Lavrov said, cited by Russia's Interfax news agency.

Moscow enjoys close trade ties with its Soviet-era ally, signing a new warplane delivery contract with Damascus this month and still leasing a Syrian port for its navy.

Gulf states and Turkey on Saturday called for global efforts to bring the bloodshed in Syria to an 'immediate end' and pave the way for a political transition.

Britain, France and Germany all called for a speedy UN resolution on Syria, with Paris saying it 'vigorously condemns the dramatic intensification of violence'.

Syrian Interior Minister Mohammed al-Shaar said the authorities were determined to 'cleanse' the country and restore order.

"The security forces are determined to carry on the struggle to cleanse Syria of renegades and outlaws... to restore safety and security," SANA quoted Shaar as saying.