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. The blast left a huge crater in a street and damaged nearby vehicles.

There were no immediate claims of responsibility. The government has blamed “terrorists” for much of the deadly violence that has continued since anti-government protests began over a year ago.

Meanwhile, a group of U.N. observers left their Damascus compound Saturday for an undisclosed location. A handful of monitors have arrived in the country to assess compliance with a peace plan brokered by international envoy Kofi Annan.

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