BEIRUT (AP) — A suicide bomber who targeted a hospital in a Syrian coastal city the previous day killed 43 people, the World Health Organization said Tuesday, as an activist group raised the overall death toll from the day's unprecedented wave of attacks on government strongholds to 154.

Most of those killed in Monday's explosion at the Jableh National Hospital in the city of Jableh were patients and visiting family members, but three doctors and nurses were also among the dead, said WHO.

The hospital, which was taking in victims from at least three other blasts that hit in the city on Monday — including one at a crowded bus station — was badly damaged and is no longer operational, WHO also said.

The wave of bombings, claimed by the Islamic State group, struck in Jableh and the city of Tartus, also on Syria's Mediterranean coast. Both cities are government strongholds that have so far remained mostly immune to the violence of Syria's civil war, now in its sixth year.

Syrian government officials said at least 80 died in Monday's devastating assaults, while the Britain-based Syrian Observatory for Human Rights, which tracks the conflict through a network of activists on the ground, said on Tuesday that 154 were killed.

The attacks signified a major breach in the security of President Bashar Assad's coastal strongholds.

The Islamic State group cast the attacks in starkly sectarian terms. A message attributed to the extremists that was circulated on social media said the bombings struck at the "home of the Nusayris," a pejorative term for Assad's minority Alawite sect.

However, Tartus and Jableh are both diverse cities, home to a sizable Sunni, Christian and Shiite population. The attacks targeted public spaces used by residents of all sects.

The bombings sparked a reprisal attack on a camp for those internally displaced by war located in Tartus. Parts of the al-Karnak camp were burned down, according to Ghassan Hassan, who heads the Tartous2day media agency. Most of the 700,000 refugees in Tartus, from Syria's northern provinces, are Sunni.

The coastal region has been the backdrop to some of the war's darker junctures, including twin massacres in Baniyas and Bayda, two formerly restive towns about 25 miles (40 kilometers) north of Tartus. Pro-government forces or militias summarily executed 248 civilians and looted and burned down Sunni neighborhoods there in May 2013, according to Human Rights Watch. The New York-based monitoring group said the methods suggested that the attackers intended to drive the Sunni population out of the towns.

Moderate and ultraconservative Sunnis now form the backbone of the rebel movement against the government in the surrounding regions.

Syria's conflict, which began as a popular uprising against Assad's government in 2011, quickly descended into a full-blown civil war. Al-Qaida militants exploited the chaos to establish a foothold in the country, but the Sunni extremist group soon fractured, spawning the powerful Islamic State group. IS now controls a large swath of territory in the northeast and has proclaimed its self-styled "caliphate" on territories it holds in Syria and Iraq. Al-Qaida remains a major player in Syria's conflict through its affiliate, the Nusra Front.