A bomb rocked the Damascus neighbourhood of Qaboon during the night killing five people, the Syrian Observatory for Human Rights said on Tuesday.
The Britain-based group gave no further information on the deadly explosion but said powerful blasts were also heard overnight in several regions across the country, including central Hama, northern Aleppo and the coastal cities of Banias and Latakia.
It added that regime forces overnight and at dawn also carried out a series of raids and arrests in various areas, including the capital's suburbs of Douma, Harasta and Barzeh as well as in Aleppo.
Demonstrations broke out at dawn in several neighbourhoods of Aleppo, the country's second city and commercial hub which until recently had been largely spared the unrest shaking the country since March last year, the Observatory said.
One person was killed by gunfire in Nouaymeh, a town in the southern province of Daraa, the watchdog said.
On Monday, at least 54 people, including 31 soldiers were killed in violence across the country, according to the Observatory.
UN chief Ban Ki-moon warned that the search for peace in Syria was at a "pivotal moment" and expressed strong concerns of an all-out civil war, as a five-week-old truce was broken yet again.© ANP/AFP