At the United Nations, Russia criticised a U.S.-drafted resolution authorising an advance team to monitor the fragile ceasefire which aims to end 13 months of bloodshed during the uprising against Assad, an ally of Moscow.
However, Western missions said the Security Council would vote on the resolution later on Friday.
Syrians took to the streets across the country in small demonstrations, trusting that the two-day-old truce which is meant to lead to political dialogue would protect them from the army bullets that have frightened off peaceful protesters for months.
Activists said security forces came out in strength in many cities to prevent protesters forming major rallies against Assad, even though the plan of U.N.-Arab League envoy Annan says the government should have pulled its troops back.
Protesters questioned Assad's commitment to the peace plan which he has accepted. In the Qadam district of Damascus, they held up a placard saying: "Bashar may be able to laugh at the whole world - except for the Syrian people". Another read: "The new comedy is the ceasefire".
The British-based Syrian Observatory for Human Rights and the anti-Assad Local Coordination Committees said two people were killed as marchers tried to converge on a central square in the city of Hama.
Troops also shot one person dead as worshippers left a mosque in Nawa in the southern Deraa province, where the uprising began. Security forces killed a third in the town of Salqeen in the northwestern province of Idlib, they said, and a fourth died in Deraya, Damascus province.
However, Syria's state news agency SANA blamed two of the deaths on the opposition, saying an "armed terrorist group" shot dead the man in Salqeen and attributing the death of the Hama protester to a shot fired by a fellow demonstrator.
It also said "terrorists" shot an army major dead as he drove to work. Armed groups were seeking to "destroy any effort to find a political solution to the crisis" in Syria, SANA said.
The United Nations estimates that Assad's forces have killed more than 9,000 people since the uprising began. Authorities blame the violence on foreign-backed militants who they say have killed more than 2,500 soldiers and police.
NO MASS RALLIES
Assad's opponents had called for mass rallies on Friday to test whether the authorities would tolerate a return to peaceful protests, as Annan's six-point plan said they should.
But rallies videoed by activists were far smaller than the huge, chanting crowds seen in major cities at the start of the uprising 13 months ago and on several occasions in 2011.
International pressure has grown for Syria to fulfil all its commitments to the former U.N. chief by withdrawing troops and heavy weapons, permitting humanitarian and media access, releasing prisoners and discussing a political transition.
Moscow's U.N. Ambassador Vitaly Churkin suggested it may take time to agree on the draft Security Council resolution authorising the advance team of 30 U.N. observers.
U.N. diplomats say Russia supports Annan's peace efforts but is working hard to shield Damascus from what it fears is a Western push for Libyan-style "regime change." Russia and China have vetoed two resolutions condemning Assad's assault on anti-government protesters.
The draft was a response to Annan's request that the Council move quickly to get the first members of an observer force that will ultimately have up to 250 monitors on the ground.
"Certainly the kind of draft that we see ... requires a lot of work and it (is) not in line with our original understanding of doing something very quickly today in order to put some people on the ground, a limited number of people," said Churkin.
The U.N. missions of Britain, France and Germany said the Security Council planned to vote on the resolution on Friday.
So many Syrians have fled the violence that neighbouring Turkey has begun accepting international aid to help share the cost of the caring for the nearly 25,000 refugees, including rebel fighters, who have crossed the border.
Jordan is also housing almost 100,000 Syrian refugees, many more than the U.N. refugee agency UNHCR has registered, the foreign ministers of Turkey and Jordan told a joint news conference in Istanbul.
French President Nicolas Sarkozy said Assad's ceasefire declaration was insincere and renewed a call for the creation of aid passages, without saying how these could be protected.
"I firmly believe the international community should live up to its responsibilities and create the conditions for humanitarian corridors so that these poor people who are being massacred can escape a dictator," he told TV channel i>tele.
Sarkozy said he had discussed Syria and the observer plan with U.S. President Barack Obama on Thursday.
Annan's spokesman Ahmad Fawzi would not name countries that would contribute the observers, but said in Geneva many already had staff in the region, who could move swiftly.
Syrian Foreign Ministry spokesman Jihad Makdissi said a U.N. technical team that was in Damascus last week would return to the capital on Friday for more talks on a protocol under which the observer mission could be deployed.
The draft resolution threatens possible future action against Syria, saying the Council "expresses its determination, in the event that the Syrian government does not implement its commitments, to consider further measures as appropriate".
Fawzi urged action on the other points of Annan's plan, especially the withdrawal of Syrian armed forces from populated areas, a condition that Syria was supposed to meet in the 48 hours leading up to the ceasefire deadline.
"We are worried about the operational deployment of heavy armour in population centres," he said. "They didn't belong there in the first place and they don't belong there now."
"We are thankful that there's no heavy shelling, that the number of casualties are dropping, that the number of refugees crossing the border are also dropping."
Underlining the fragility of the truce, Fawzi confirmed there had been some clashes. "Sometimes in situations like this the parties test each other ... one shot, one bullet, can plunge Syria back into the abyss," he said.