Syrian soldiers have fired bullets and tear gas to disperse thousands of protesters, activists said, as state media reported a deadly roadside bomb explosion, in the latest violence to defy international efforts to calm the country's crisis.
Protesters on Friday spilled out from mosques onto the streets in cities and towns across Syria, calling for the downfall of President Bashar al-Assad, chanting in support of the country's opposition armed forces, activists said.
The Local Co-ordination Committees, an opposition activist network, reported the deaths of at least 36 people, including three children.
Meanwhile, state television agency said 10 security personnel were killed by a roadside bomb planted by "terrorists" in Sahm al Golan village in the southwest of the country.
It said that the bomb weighed 100kgs but gave no other details.
A ceasefire plan, drafted by former UN chief Kofi Annan, technically went into effect last week, but has been steadily unravelling. Both the government and the opposition blame each other for violating the truce.
Ban Ki-moon, the UN Secretary-General, said Damascus was not honouring the ceasefire and that violence was escalating.
Ahmad Fawzi, Annan's spokesperson, said: "During the course of next week we hope that those that we are seconding from missions in the area who can move quickly will be there and we will make the numbers up to 30."
Only seven of the 30-men strong advance mission have so far arrived in Syria, and the Security Council must pass a resolution allowing the full mission which could number up to 300.
The preliminary agreement between the UN and the Syrian government states that observers will have freedom to go anywhere in the country by foot or by car, take pictures, and use technical equipment to monitor compliance of the truce.
In-depth coverage of escalating violence across Syria
But in a move likely to anger the opposition, the head of the team currently in Syria said they will not patrol on Fridays, the day of the week when the biggest numbers of protesters normally takes to the street.
"We don't want to be used as a tool for escalating the situation. So we will avoid going on patrols on Fridays," Colonel Ahmed Himmiche, from Morocco, said.
Protests were reported in the capital Damascus and its suburbs, as well as in the northern city of Aleppo, the central regions of Hama and Homs, in eastern towns near the border with Iraq and in the southern Daraa province.
"Security is extremely tight in Damascus," said activist Maath al-Shami, adding that despite the wide presence of plainclothes security agents, there were protests in the capital's neighborhoods of Qaboun, Midan, Barzeh and Mazzeh.
Shelling was reported in several neighbourhoods of Homs, the central city where government forces have been fighting armed opposition groups for months.
The Local Co-ordination Committees said at least 12 people were killed there.
It also reported the deaths of nine people in the northwestern province of Idlib, seven in Damascus, four in Aleppo, two in the Damascus suburbs of Douma, one in Qamishli and one in Deraa.
According to the UN, more than 9,000 people have been killed since the uprising Assad began 13 months ago.
On Thursday, the US secretary of state called for the Security Council to adopt an arms embargo and other tough measures against Syria.
Addressing the so-called Friends of Syria group in Paris on Thursday, Hillary Clinton stopped short of calling for outside military intervention, but said it was time to impose more consequential measures on Assad if his country failed to abide by the peace plan.
"We have to keep Assad off balance by leaving options on the table,'' Clinton said.
"We need to start moving very vigorously in the Security Council for a Chapter 7 sanctions resolution, including travel, financial sanctions, an arms embargo, and the pressure that that will give us on the regime to push for compliance with Kofi Annan's six-point plan."
Under Annan's plan, the Syrian government is required to pull troops and heavy equipment out of towns and cities - which Ban said it has not done.
Thursday's agreement obliges the troops to return to barracks located "a minimum of 2-3 kilometres outside the perimeter of these population centres".
According to the deal, the Syrian government must allow unhindered access of UN personnel to facilities, locations, individuals and groups considered of interest.
As for the opposition, the agreement states that Annan must confirm that opposition fighters stop "all acts of aggression against Syrian army formations, bases, convoys and infrastructure ... against government agencies, buildings, infrastructure as well as private and public properties" and "commit to stop all illegal activities ... including assassinations, kidnapping or vandalism".
At their meeting in Paris, the Friends of Syria group called the peace plan the "last hope" to resolve the Syrian crisis, but cautioned that they were ready to consider "other options" if Annan's mediation efforts broke down.
Foreign ministers of countries including France, the US, Saudi Arabia and Qatar said they would do everything to ensure the plan succeeded.
"Every day that passes means tens of new Syrian civilian deaths," Alain Juppe, France's foreign minister, said as he read out the conclusions of the meeting.
"It is not time to prevaricate. It is time to act. Though fragile, the Annan mission represents a last hope.
"If this were not to happen ... the UN Security Council and international community would have to look at other options."
Russia and China, two of Syria's strongest allies, were absent from the Paris meeting.