Kofi Anna, the international envoy for Syria, has told the UN Security Council that Syria has not fully complied with the terms of his peace plan, despite observing a cease-fire that went into effect at the start of the day.
Speaking in New York, Annan urged the council to demand that Syria full comply by withdrawing troops and heavy weapons from towns as agreed in the peace deal.
Earlier in the day, UN Secretary-General Ban Ki-Moon said that the situation in Syria looked calmer after a UN-brokered cease-fire went into effect.
"As of this moment, the situation looks calmer. We are following it very closely," Ban said. "The world is watching, however, with skeptical eyes since many promises previously made by the government of Syria have not been kept."
Speaking in Geneva, Ban also said further militarization of the conflict is not the solution and that he is working with the UN Security Council to send an observer team to Syria as quickly as possible.
Under the deal brokered by Annan, the cease-fire is to be followed by the deployment of an observer mission and negotiations between Syrian President Bashar al-Assad's government and the opposition on a political transition.
There were reports of scattered violence across the country. Activists said forces loyal to Assad fired on civilians in several places, killing at least three people.
Meanwhile, state media said a roadside bomb in the central city of Aleppo killed one army officer and wounded 24 officers and cadets.
Despite the cease-fire, government troops have not pulled back to barracks, as stipulated by Annan's peace plan.
"What we see today, this morning, is that the heavy weaponry is stationed everywhere inside the populated areas," Basma Kodmani, a spokeswoman for the Syrian National Council, the main political opposition group, told journalists in Geneva. "Snipers are deployed across the country in all the populated areas and the centers. There has been an increase, a big increase, in the number of checkpoints, and those checkpoints are heavily armed."
The relative lull follows weeks of escalating attacks on opposition strongholds by Assad's regime.
Still, expectations were low for an abrupt end to the violence that has rocked the country for more than a year and claimed more than 9,000 lives.
"[Assad's] words are all gibberish," a Syria refugee, Hussein Kasib, told Reuters at the refugee camp at Yayladagi, Turkey. "This cease-fire will not last long. He has been promising this for a year. I do not think he will withdraw either tanks or troops. He is lying. Whenever he says he will end the massacre, he kills more."
Syria and the armed opposition have said they will abide by the cease-fire but were ready to respond if attacked.
The Syrian Interior Ministry said on April 12 that gunmen "who do not have blood on their hands" should turn themselves in to police in the knowledge they will be set free.
Under Annan's plan, the cease-fire is to be followed by the deployment of an observer mission and negotiations between Assad's government and the opposition on a political transition.
China's Foreign Ministry welcomed Syria's pledge for a cease-fire and called on the government to "take concrete actions to support and cooperate with Annan's mediation efforts."
It also called on the opposition to honor the agreement and work toward a political settlement of the crisis.
China, along with Russia, has vetoed two resolutions condemning the crackdown in Syria, but both are backing Annan's mission.
With reporting by Reuters, AFP, AP, and dpa