Syrian troops held their fire in the hours after a U.N.-backed ceasefire took effect at dawn on Thursday, casting a silence over rebellious towns they had bombarded heavily in recent days.
But the lull did little to convince opposition activists and Western powers of President Bashar al-Assad's good faith in observing a peace plan agreed with international envoy Kofi Annan. In defiance of that deal, Syrian troops and tanks were still in position inside many towns, activists told Reuters.
A report on state media that a terrorist bomb blasted an army bus and killed a senior officer in Aleppo after the truce began raised a possibility troops will keep a pledge to hit back. State media also reported a bomb wounding officers near Idlib and a ruling party member shot dead in Deraa in the south.
The Syrian government bars access to most independent media.
The exile opposition called the ceasefire only partially observed due to the army's failure to leave the streets and its leader urged a renewal on Friday of peaceful protests, which have been subdued of late by fear. But he warned those who might take part that they could expect government forces to open fire.
The Interior Ministry urged rebels to surrender, promising to free those who had not killed, and broadcast an appeal to the thousands who fled battered cities like Homs and Hama to return from the havens they found in Turkey, Lebanon and within Syria.
But streets in troubled towns remained nervously empty. An exile opposition spokeswoman said three people had been killed during the morning by security forces, and dozens more arrested.
Speaking after the 6 a.m. (0300 GMT) U.N. deadline passed, Abu Rami, an activist in Homs said: It was a bloody night. There was heavy shelling on the city ... But now it is calm, and there is no shooting. Assaults on restive neighbourhoods had become more intense after Assad accepted Annan's timetable.
Government spokesman Jihad Makdissi, speaking before the report of the bombing of the army bus, said Damascus was fully committed to Annan's success and that there would be no breach of the ceasefire by the government if the rebels did not attack.
At the United Nations, Annan was to brief the deeply divided Security Council at 1400 GMT, though diplomats expect a full report from him only on Monday. Western powers, though hesitant to intervene militarily, are lobbying Russia, a key ally for Assad, to drop its veto on other U.N. measures to pressure Syria into abandoning four decades of autocratic rule by his family.
The 13-month crisis has pushed pressure waves out along faultlines that criss-cross the Middle East, pitting Sunni Arabs against Shi'ite Iran, and alarming Turkey, whose prime minister on Thursday cited his country's right to call on its NATO allies to defend a border where Syrian troops opened fire this week.
People contacted in the flashpoint provinces of Homs, Hama and Idlib, which saw sustained shelling by Assad's forces over the past week, reported calm. Damascus too seemed quiet.
Snipers, tanks and soldiers are still there. They haven't gone anywhere, said an activist in Homs named Yazan. People are wary and they believe that this ceasefire is only temporary.
Nobody is leaving their home.
Burhan Ghalioun, exile head of the opposition Syrian National Council (SNC), told Reuters he expected demonstrations on Friday after weekly prayers - a feature of the revolt that had been subdued by violence in recent months. But he did not trust the authorities who had their hand on the trigger.
The Syrian people will go out tomorrow in the biggest possible numbers so that the Syrian people can express their will, Ghalioun said. While we call on the Syrian people to protest strongly... we ask them to be cautious because the regime will not respect the ceasefire and will shoot.
A Norwegian general who has spent the past week in Damascus discussing a planned U.N. peace observer mission said he was cautiously optimistic. But Major-General Robert Mood, who was briefing Annan in Geneva, told Norway's NTB news agency: Both sides are plagued by a very high degree of mutual suspicion.
It's terribly difficult for them to cross that abyss.
Annan's plan has been for about 250 unarmed U.N.-mandated observers to monitor the ceasefire. A similar Arab League mission ended in disarray amid mounting violence in January.
Spokesman Makdissi told the BBC Syria wanted the monitors to start as soon as possible to monitor any possible violations.
Basma Kodmani, a spokeswoman for the SNC in Geneva, said even without monitoring there was ample video and eyewitness evidence showing troops were still out in force in town centres: The real test today for us is if people can go down and demonstrate peacefully, she said. This is the reality check.
Highlighting the wider international ramifications of a crisis that has divided world powers along Cold War lines, British Prime Minister David Cameron said Assad was failing to abide by the terms endorsed by the U.N. Security Council:
I feel an immense sense of frustration because the world has come together behind this Kofi Annan plan, he told the BBC. This is a plan, remember, that is not just backed by those of us who have been pushing for action on Syria, it's also backed by China and Russia. And yet Assad is deliberately flouting it.
In an indication of how the Western leaders who intervened to help rebels topple Muammar Gaddafi in Libya last year are reluctant to do likewise in Syria, Cameron made it clear that the main thrust of Western efforts would still be to persuade Moscow and Beijing to accept tighter diplomatic sanctions.
Now is the time to say to the Russians and Chinese, look at the man we are dealing with, look at the appalling way he is behaving, Cameron said. We need to go back to the U.N. and tighten the pressure, tighten the noose.
CHINA HAILS CEASEFIRE
Russia and China, alarmed by the way last year's Security Council resolution on Libya led to military intervention against a sovereign state, have vetoed attempts to penalise Assad, although the United States, European Union and Arab League have imposed their own economic and political sanctions.
China's Foreign Ministry called on the opposition to honour the truce, something the disparate rebel movements have said they are willing to do - although Western leaders and Annan's team have made clear the onus is on the government to act first.
China welcomes the government's relevant decision, which will help to ease tensions, the ministry said in a statement. China also calls on the Syrian armed opposition to immediately cease fire and implement Annan's six-point proposal.
Annan's spokesman stressed on Wednesday that all elements of the plan must also be respected - notably Item 2, which calls for armed forces to withdraw from the vicinity of urban areas.
Syria's Defence Ministry said on Wednesday it would halt operations but made no mention of an army pullback from cities and said it would confront any assault by armed groups.
The U.S. ambassador to the United Nations, Susan Rice, said the commitment could not be construed as complying with the former U.N. secretary-general's peace plan: The caveats in the letter are worrying, she said. But nothing casts more doubt on the credibility of the commitments than the fact that commitments have been made and made and made and broken and broken and broken, she said on Wednesday, noting that attacks had intensified since Assad agreed to the plan two weeks ago.
The Syrian rebels were also sceptical of Assad's intentions.
The Defence Ministry announcement is a deviation from Annan's plan, which clearly says he should pull back the tanks and end violence, Qassem Saad al-Deen of the Free Syrian Army said on Wednesday, adding that the fighters would give the truce a chance but could respond if the government broke it.
It is unclear how far FSA commanders, the SNC or any of the other elements of the opposition can control fighters in Syria.
Assad's forces have killed more than 9,000 people in the past year, according to a U.N. estimate. Damascus says rebels have killed more than 2,600 soldiers and security personnel.
(This story has been corrected to fix a typo in paragraph 3)
(Additional reporting by Louis Charbonneau and Michelle Nichols at the United Nations, Stephanie Nebehay in Geneva, Oliver Holmes and Douglas Hamilton in Beirut, Michael Holden, Philippa Fletcher and Alison Williams in London and Balazs Koranyi in Oslo; Writing by Alastair Macdonald; editing by Philippa Fletcher)