Clashes between government forces and rebels fighting to overthrow President Bashar al-Assad raged overnight in Syrian towns and flared again during the day, said the Syrian Observatory for Human Rights.
Despite an initial pause in fighting on April 12, a promised ceasefire has not taken hold. Nor has the carnage in Syria stopped, despite a parliamentary poll on Monday which the government promoted as a milestone on its path to reform but the opposition dismissed as a sham and boycotted.
Speaking to reporters in Geneva after briefing the U.N. Security Council via video link, Annan said there were "worrying episodes of violence by the government" in Syria as well as attacks by the opposition in violation of the truce. He described a recent spate of bombings as "really worrying."
He urged Damascus and the rebels to revive the truce.
"If you can do it for one day, why don't you do it for a week, a month, why don't you give peace a chance and give the people of Syria a break?" Annan said. "Why do they have to put up with this trauma?"
"There is a profound concern that the country could ... descend into full civil war and the implications of that are quite frightening," he said. "We cannot allow that to happen."
Annan's comments were likely to deepen doubts about Damascus' commitment to the former U.N. secretary-general's peace plan and could fuel fears among Western powers on the 15-nation council that it has little chance of success.
U.S. Ambassador to the United Nations Susan Rice said after the council meeting that "the Syrian government has not implemented fully any of the six points of the Annan plan."
"The situation in Syria remains dire, especially for the millions who continue to endure daily attacks and who are in urgent need of humanitarian assistance," Rice said.
"We are increasing our support to unify and strengthen the opposition through non-lethal assistance."
The United States has said it is already giving the Syrian opposition logistical and communications help, but it has shied away from providing arms.
The International Committee of the Red Cross said fighting had been so intense in some parts of Syria that it was starting to look like civil war in some places.
Jakob Kellenberger said he was very worried about conditions in Syria, where unarmed United Nations observers are being deployed to monitor a ceasefire agreement that has been repeatedly violated by both state forces and by rebels.
"I really hope that the U.N. observers will deploy rapidly," he told reporters in Geneva, indicating concern for the fate of Annan's peace plan. "I still hope it will not fail."
SYRIA DISPLAYS CD OF "CONFESSIONS"
Russian U.N. Ambassador Vitaly Churkin, however, was optimistic. "Things are moving on in a positive direction. Many obstacles, but I think they can be overcome," he said.
The United States and European members of the Security Council have said they would urge the Security Council to impose sanctions on Syria if it does not fully withdraw its heavy weapons and troops from Syrian towns and stop the fighting. But Russia and China have hinted they would veto any sanctions move.
Syrian U.N. envoy Bashar Ja'afari also spoke of a "positive trend on the ground" and blamed foreign powers for the violence.
Ja'afari displayed a CD that he said contained 26 confessions from Arabs who were caught in Syria and had come from Libya, Tunisia and elsewhere through Turkey and Lebanon "to perpetrate terrorist acts in Syria." He said another 15 foreign fighters had been killed by Syrian security forces.
The Syrian ambassador urged Saudi Arabia, Qatar and Turkey to stop "their sponsorship of the armed rebellion."
Arab League chief Nabil Elaraby called for continued support of Annan's plans and expressed similar concerns over civil war.
Beyond the ceasefire and monitoring mission, Annan's plan also calls for free access for journalists, humanitarian aid access and political dialogue between the government and opposition. So far, 60 of some 300 monitors have arrived with the whole team expected to be assembled by the end of May.
The British-based Observatory said security forces were using rockets and heavy machine gun fire on the village of al-Hassan in the rebellious central Homs province, as they sought to wrest control from rebels in the area.
A similar bombardment in northern Idlib province killed at least three people, it said.
The United Nations says more than 9,000 people have been killed by state forces trying to crush the revolt against four decades of rule by Assad and his father, Hafez al-Assad.
What began as a peaceful protest movement has been overtaken by an armed insurgency against Syrian forces. The government says the rebels are terrorists steered by foreign powers and more than 2,600 police and army personnel have been killed.
Despite Syria's bloodshed, the state news agency SANA reported a "notable" turnout for Monday's vote. Many residents in Damascus said few Syrians voted, and a Reuters team at a polling booth saw only three ballots cast over 40 minutes.
Initial results reported by the pro-government Syrian channel al-Ikhbariya suggested that around 700,000 people voted in Aleppo, the most populace city and province in Syria.