A series of explosions rocked Syria on Saturday, leaving at least five people dead as U.N. observers continued efforts to monitor a frayed cease-fire between the government and the opposition.

The Syrian Observatory for Human Rights says five people were killed in the northern city of Aleppo after an explosion ripped through a car wash as a bus was passing by.

Activists say two blasts shook Damascus, including one caused by a bomb planted under a military vehicle.

There were no immediate claims of responsibility.

Meanwhile, about 40 U.N. observers are in Syria assessing compliance with a peace plan brokered by international envoy Kofi Annan.

In an interview with VOA, the head of the U.N. mission in Syria, Norwegian General Robert Mood said the observers have seen a “calming effect” in areas where they have deployed. He said the U.N. team has seen a significant reduction in shooting and shelling.

The observers have visited such areas as the flashpoint Hama region, Homs, Idlib, Daraa and Damascus.

The U.N. mission hopes to have 300 observers in Syria by the end of this month.

The United Nations estimates at least 9,000 people have been killed in the crackdown on the opposition, while the government says it has lost at least 2,600 of its forces to “foreign-backed terrorists.”

The violence has been ongoing since anti-government protests in Syria began more than a year ago.

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