UN chief Ban Ki-moon and his envoy were encouraged that a ceasefire appears to be holding in Syria, but urged its government to keep its promises and said a single gunshot could derail the fragile peace.
Mr Ban told a news conference in Geneva that it is mainly up to Syrian President Bashar Assad's regime to keep its promise and hold to a ceasefire. "As of this moment the situation looks calmer. We are following it very closely," Mr Ban said.
"The world is watching, however, with sceptical eyes, since many promises previously made by the government of Syria had not been kept. The onus is on the government of Syria to prove that their words will be matched by their deeds at this time," he said.
His envoy, Kofi Annan, said the UN was asking for a speedy deployment of an observer mission to help keep the cease-fire going.
Shortly after the 6am deadline passed this morning, there was no sign of heavy shelling or rocket attacks in Syria. But a civilian was reported killed and Syria's state-run news agency said "terrorist groups" launched a roadside bomb that killed a soldier.
Mr Ban urged Assad's government to keep its promises since it has previously failed to observe an internationally brokered cease-fire since launching a crackdown on mass protests more than a year ago.
"This ceasefire process is very fragile. It may be broken any time," Mr Ban said. "If and when there is another gunshot, even a small gunshot may give both sides the pretext to engage in another fighting. This is a very worrisome."
Mr Annan, also in Geneva, said in a statement that he also was encouraged that the ceasefire in Syria appears to be holding and urged the government and rebels to fully implement his 6-point peace plan.
Mr Ban called on Assad to hold to the plan and on the opposition "to sustain this cessation of violence in all its forms."
Mr Annan stressed just before his closed-door briefing by videoconference to the UN Security Council that the plan includes military provisions requiring the withdrawal of troops and heavy military equipment from towns and cities and a commitment to move to a political process.
The council was being asked to approve the deployment of a UN observer mission as soon as possible to allow for "a serious political dialogue" to be launched quickly.
"It is difficult to fully assess the situation on the ground, in the absence of UN observers. And therefore we are working with the Security Council to send an observer team as promptly as possible," Mr Ban told reporters.
The council's major powers - the US, China, Russia, Britain and France - all hold veto power on the 15-nation council where Russia has served as Syria's key ally.
"If we are to stop Syria's descent into chaos, the international community must speak and act as one," Mr Ban said.
Mr Annan's spokesman, Ahmad Fawzi, has told reporters in Geneva the mission would have about 200 to 250 observers and nations were being asked to contribute soldiers.
Mr Ban said the observer mission could get going almost as soon as it gains authorisation and that he expects Russia to support it, based on talks with Foreign Minister Sergey Lavrov on Wednesday.