The Syrian defence ministry said 36 people were killed and more than 50 wounded Wednesday in Israeli air strikes on the city of Palmyra, renowned for its ancient ruins.
The Syrian Observatory for Human Rights, a Britain-based war monitor, said the Israeli strikes had killed as many as 61 people.
"The Israeli enemy launched an air attack from the direction of the Al-Tanf area, targeting a number of buildings in the city of Palmyra," the defence ministry said in a statement, AFP reports.
The attack "killed 36 people and wounded more than 50", and caused "significant material damage," it added.
The Syrian Observatory for Human Rights however gave a higher toll, which it expected to "rise due to the presence of seriously injured people".
"The total number of dead reached 61 people," it said.
Among them, 33 were Syrians affiliated with Iranian militias, 22 were non-Syrians, four from Hezbollah and two unknown, according to the monitor.
The strikes targeting Palmyra -- a modern city adjacent to Greco-Roman ruins -- are the deadliest in Syria since all-out war erupted between Iran-backed Hezbollah and Israel on September 23.
Israel rarely comments on individual strikes in Syria but has repeatedly said it will not allow Iran to expand its presence in the country.
The Syrian Ministry of Foreign Affairs condemned "in the strongest terms the brutal Israeli aggression against the city of Palmyra, which reflects the continuing crimes of Zionism against the countries of the region and their peoples".
Palmyra, a UNESCO World Heritage Site, was taken over and pillaged by Islamic State jihadists at the height of the Syrian civil war.
The director general of Antiquities and Museums in Syria, Nazir Awad, told AFP the city's temples "did not suffer any direct damage" during the latest strikes.
"We need to conduct a survey on the ground to confirm these observations," he added.
