BEIRUT (Reuters) - Syrian opposition activists called mass protests for Friday to test a fragile, day-old ceasefire by President Bashar al-Assad’s forces, and international pressure mounted for Damascus to fully comply with a U.N.-backed peace plan.

Anxious to build on a truce between the armed forces and rebels which brought an eerie calm to Syria on Thursday, after more than a year of clashes, the U.N. Security Council worked on a resolution authorizing U.N. observers to monitor it.

World leaders welcomed the halt in fighting which had threatened to spill over into neighboring countries and U.N. Secretary General Ban Ki-moon said the situation looked calmer.

“The world is watching, however, with skeptical eyes since many promises previously made by the government of Syria have not been kept,” he told a news conference in Geneva.

Along with the withdrawal of forces from population centers, U.N.-Arab League envoy Kofi Annan’s six-point plan calls for talks with the opposition aimed at a “political transition”, the release of political prisoners, access for humanitarian aid and journalists, and for the authorities to “respect freedom of association and the right to demonstrate peacefully”.

Burhan Ghalioun, head of the opposition Syrian National Council (SNC), said he did not trust the authorities to allow the renewal of protests after Friday prayers, a feature of the uprising that has been subdued by violence in recent months.

The authorities, he said, had their “hand on the trigger”.

“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,” he told Reuters.

AUTHORISED PROTESTS

The Syrian Interior Ministry said only pre-authorized demonstrations would be permitted by police, a caveat which the opposition said did not bode well.

“This is ridiculous,” said an activist called Musab from Hama city, a focus of opposition activity and government bombardment along with Homs and Idlib. “They will not give you permission and you will be taken to jail if you ask for it”.

He said a demonstration on Wednesday in the town of Qalat Madiq, in Hama province, had been broken up by security forces firing, and nine people were arrested. Most independent media are banned from Syria, making such reports impossible to verify.

In Homs, where opposition stronghold districts were all but deserted, activist Yazan expressed doubt people would dare to go out because snipers, tanks and soldiers were still in place. “People are wary and they believe that this ceasefire is only temporary. Nobody is leaving their homes,” he said.

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The SNC’s spokesman said Assad could simply not afford to stop shooting, since that would allow a new wave of mass protests against his family’s four decades of absolute power.

“As soon as there is a real ceasefire, people will come out to the streets, demonstrating and demanding his removal, his stepping down. So I think the regime has to retaliate by opening fire again,” spokesman Bassam Imadi told Reuters in Istanbul. “But let’s hope for the better.”

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OBERVER DEPLOYMENT

Annan, mandated by the United Nations and Arab League, has called for 200 to 250 unarmed U.N. observers to monitor the ceasefire.

A similar Arab League mission ended in disarray amid mounting violence in January, but Russia’s U.N. Ambassador Vitaly Churkin said the 15-member Security Council could adopt a resolution authorizing the deployment of a U.N. observer force as early as Friday.

“The full-fledged mission will take some time to deploy ... If we are able to put 20 or 30 monitors (there) early next week, very good,” Churkin said. “If we are able to put more in the next few days that’s even better.”

A draft resolution drawn up by the United States would have the Council authorize an initial deployment of up to 30 observers and demand the withdrawal of troops and heavy weapons from population centers and an end to violence on all sides.

It included a vague threat of future action against Damascus, saying the council “expresses its determination, in the event that the Syrian government does not implement its commitments, to consider further measures as appropriate”.

It was not immediately clear how Russia and China, which vetoed two previous resolutions condemning Assad’s 13-month assault on anti-government protesters, reacted to the draft, which diplomats discussed behind closed doors on Thursday.

Most of the demands in it were addressed to the Syrian government, which could irritate Moscow and Beijing. Both have welcomed the ceasefire while emphasizing the requirement for rebel forces to comply.

The United States and European Union have imposed their own sanctions against Damascus after failing to persuade Russia and China to join in.

Moscow and Beijing are wary of further U.N. moves, alarmed by the way last year’s Security Council resolution on Libya led to military intervention, though Western leaders are also cautious about intervening in Syria’s mix of religious and ethnic groups.

Ban said there had been a surge in Syrian refugees fleeing to Turkey and Lebanon this week and an estimated 1 million people inside Syria now needed humanitarian assistance.

He was urging Assad to keep his promise and to exercise maximum restraint, he said.

“This ceasefire process is very fragile - it may be broken any time if, and when, there is another gunshot,” Ban said. “This is a very worrisome.”