An additional 30 United Nations monitors should arrive in Syria in the coming week to join an advance team of seven observing a fragile week-long cease-fire which has failed to end bloodshed in the country, a spokesman for envoy Kofi Annan said on Friday.

At least 23 people were killed, 10 of them in a roadside bomb targeting security forces near the Golan border and most of the others in shelling by President Bashar Assad's forces on the city of Homs, further undermining the truce.

Open gallery view Demonstrators protest against Syria's President Bashar Assad after Friday Prayers in Kafranbel, near Idlib April 20, 2012. Credit: Reuters

With Friday prayers a weekly flashpoint for unrest, the monitors decided to remain indoors, saying they wanted to avoid being "used as a tool for escalating the situation". A day earlier they were mobbed by anti-Assad protesters on their initial forays around the country.

Peace envoy Kofi Annan's deputy, former Palestinian foreign minister Nasser al-Kidwa, criticized both sides, but particularly government forces, for refusing to stop fighting completely.

"We don't see much of a ceasefire," he told France 24 television. "The situation of course is not good. There are many reasons to be worried by the lack of implementation, at least lack of full implementation by Syrian government and perhaps some other parties as well."

Syria said 10 security personnel were killed in a roadside bomb in Sahm al-Golan in the southwest, as protests calling for the downfall of Assad broke out across the country, including in the capital Damascus.

Activists in the central city of Hama said people were wounded when security forces opened fire on protesters.

Several neighborhoods in the rebel stronghold of Homs were shelled, activists said, and the Syrian Observatory for Human Rights in Syria said at least 13 people were killed, most of them in Homs.

The UN monitoring mission is seen as the last chance to avoid civil war in Syria where Assad sent tanks and troops to quell protests against his 12-year rule, which started peacefully a year ago but have taken a militarized turn.

Annan is hoping the UN Security Council will in the next two to three days agree to send a second wave of up to 300 more observers. His spokesman said the mission was being prepared.

"We are preparing for the deployment because we feel that it is going to happen sooner or later because it must happen," spokesman Ahmad Fawzi told a news briefing in Geneva.

"The situation on the ground is not good," he said.

The Security Council - divided between Western countries that want to topple Assad, and Russia and China which support him - must agree if the larger observer team is to be sent to help quell the violence that has killed thousands of people.

While Russia circulated a draft Security Council resolution to authorize the 300-strong unarmed ceasefire force , France said it was drafting another resolution that would allow a larger observer force, with up to 500 observers as well as helicopters.

China said it was willing to contribute members to the observer team in Syria.

"We are willing to send personnel to take part in the work of this team and the advanced team. We are now in consultations with the United Nations secretariat about the specific arrangements." said Foreign Ministry spokesman Liu Weimin.

He said the overall size of the monitoring effort would have to be settled by the Security Council and so could not say how big China's contribution would be.

Top UN humanitarian official John Ging said he hoped Syria would grant permission in the coming days to send more aid workers to the country where at least 1 million people are in need of urgent assistance.

He told reporters in Geneva that Syria had recognized there were "serious humanitarian needs" and that action was required, but logistical issues and visas for aid workers are still being discussed.

On Thursday, Syria and the United Nations signed an agreement setting out the working conditions for hundreds of ceasefire observers.

The agreement stipulates "unfettered access" and freedom for monitors to travel and contact people within the framework of their mandate, Fawzi said.