Seven bombs, most of them suicide attacks, hit Syrian regime strongholds almost simultaneously, killing over 100 people.
Bomb blasts killed more than 100 people in the Syrian coastal cities of Jableh and Tartus on Monday, the British-based Syrian Observatory for Human Rights has said.
DAESH terrorists claimed responsibility for the attacks in the Mediterranean cities, saying it was targeting supporters of Syrian regime leader Bashar al Assad.
At least 53 people were killed in the city of Jableh and another 48 died in Tartus further south, where regime ally Russia maintains a naval facility, according to the SOHR.
State media reported that a car bomb and two suicide bombers attacked a petrol station in Tartus. In Jableh, one of the four blasts hit near a hospital, state media and the SOHR said.
Syrian state media also reported the attacks but said the total death toll was 78, including 45 in Jableh and 33 in Tartus.
SOHR head Rami Abdel Rahman said they were "without a doubt the deadliest attacks" on the two cities since the conflict in Syria erupted in March 2011.
Russia, which intervened in the civil war in Syria in support of Bashar al Assad last September, operates an air base at Hmeymim in Latakia and a naval facility at Tartus.
The city of Latakia, which is north of Jableh and near the Assad family's hometown, has been targeted on a number of occasions by bombings and rocket attacks.