Beirut: A huge blast ripped through the Syrian coastal city of Banias during Monday night, killing four people, while a six-year-old girl died in Damascus province, a monitoring group said on Tuesday.

"A woman and three young men were killed" in a powerful explosion in the south of Banias, the Britain-based Syrian Observatory for Human Rights said in a statement.

It said the girl died in violence in the Shehab Eddin Al Ras area of Damascus province but gave no further details.

The Observatory also gave an updated toll of 37 people killed in unrest which swept parts of Syria on Monday, including 23 soldiers killed by military defectors at Rastan, a rebel-held city in restive Homs province in central Syria.

The bloodshed came despite a ceasefire brokered by UN-Arab League envoy Kofi Annan as part of a plan aimed at ending violence that has swept Syria since March 2011 when a revolt erupted against President Bashar Al Assad's regime.

More than 12,000 people, the majority of them civilians, have died since the Syrian uprising began, according to the Observatory, including more than 900 killed since the April 12 truce.