Most of those killed in yesterday'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 yesterday - including one at a crowded bus station - was badly damaged and is no longer operational, WHO also said.
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 today that 154 were killed.
The attacks signified a major breach in the security of President Bashar Assad's coastal strongholds.
More From This Section
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.
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.