Syrian troops heavily shelled a suburb of the capital Tuesday, and satellite imagery showed that Syria has failed to withdraw all of its heavy weapons from populated areas as required by a cease-fire deal, an official said.
The shelling came hours after rebels seeking to topple President Bashar Assad killed three regime officers in separate attacks around Damascus, activists and state media said, the latest violence targeting the security forces used by the government to quash dissent.
A bomb hidden in an army truck also exploded in the capital, wounding several people.
The persistent bloodshed has tarnished efforts by a U.N. team of observers to salvage a truce that started to unravel almost as soon as it began on April 12. Despite the violence, the international community still sees the peace plan put forward by envoy Kofi Annan as the last chance to prevent the country from falling into civil war _ in part because there are no real alternatives.
Despite the bombardment, U.N. monitors visited the restive Damascus suburb of Douma on Tuesday, their second visit in two days.
The Local Coordination Committees activist group called Tuesday's barrage the "most violent shelling" of Douma since the crisis began adding that the violence left eight people dead and more than 100 wounded. The group also said that troops shelled the nearby suburb of Harasta.
Amateur videos posted online showed smoke rising into the sky as a result of the shelling.
"We are dying," shouted Douma-based activist Mohammed Saeed through Skype. "The observers are conspiring against us. Yesterday they refused to go with us to show them where the tanks are being hidden."
Annan, who was giving a speech in Sweden and briefing the U.N. Security Council in New York, called on the Syrian government to fully implement its commitments under the truce, his spokesman Ahmad Fawzi told U.N. reporters in Geneva.
"This means withdrawal of all heavy armory (weapons) from population centers and (sending them) back to the barracks. They are claiming that this has happened. Satellite imagery, however, and credible reports show that this has not fully happened, so this is unacceptable," Fawzi said.
Fawzi added that Annan is aware that when the U.N. monitors enter conflict areas in Syria that "the guns are silent," then "when they leave, the exchanges start again." He added there appear to be cases of Syrians being targeted by authorities after approaching U.N. observers monitoring the truce. Fawzi called the situation "totally unacceptable."
The observers also returned to the central city of Hama, where regime forces killed more than 30 people on Monday. The killings were apparently in retaliation for a large rally to welcome the team during a visit on Sunday.
An amateur video showed two women appealing to the team's head, Col. Ahmed Himiche, for protection.
"They slaughtered us! Our children are gone! Burning and killing and slaughter!" one woman yells, preventing Himiche from shutting the door of his white U.N. Land Cruiser. "If you really came as observers for us, have mercy on us!"
Team spokesman Neeraj Singh said the team also visited the city of Homs, where two observers are staying, and that two would remain in Hama.
The Britain-based Syrian Observatory for Human Rights said an intelligence officer was shot dead in the northeastern Barzeh neighborhood of the capital Damascus. Also Tuesday, the state news service said "terrorists" shot to death a retired lieutenant colonel and his brother, a chief warrant officer, in an area southwest of the capital.
Inside the city, explosives planted in an army truck blew up as the vehicle traveled through downtown, leaving a hole in its roof and blood and shattered glass on the road. The truck's driver and two passengers in a nearby car were injured and taken to a hospital.
The state news service said an "armed terrorist group" planted explosives under the driver's side.
No one immediately claimed responsibility for the attacks.
Activists said at least 11 people were killed in Syrian Tuesday.
The 11-person U.N. team is in Syria to observe the cease-fire and prepare for a total of 300 monitors to arrive later.
The U.N. says more than 9,000 people have been killed since the Syrian conflict began.
Associated Press writers Albert Aji in Damascus, Syria and John Heilprin in Geneva contributed to this report.