The World Health Organization says a suicide attack at a hospital in Syria's coastal city of Jableh the previous day has killed 43 people.

WHO says most of those killed were patients and their visiting family members but there were also three doctors and nurses killed in Monday's attack. The organization says the hospital is no longer working.

The bombing was part of a coordinated wave of attacks claimed by the Islamic State group in Jableh and the city of Tartus, government strongholds that have so far remained mostly immune to the violence of Syria's civil war, now in its sixth year.

Government officials have said that at least 80 died in Monday's devastating assaults, while the Britain-based Syrian Observatory for Human Rights said on Tuesday that 154 had died.