The jihadists were killed yesterday and more than 50 injured "in at least 35 air strikes targeting areas of the city of Palmyra by Syrian and Russian warplanes", the Syrian Observatory for Human Rights said.
Clashes pitting regime forces against IS jihadists raged nearby, the Britain-based group said.
IS seized Palmyra, a UNESCO World Heritage Site in eastern Syria known as the "Pearl of the Desert", last May, sending shockwaves across the world.
UN experts said the main building of the temple plus a row of columns had been destroyed.
The Syrian army and its Russian ally are reportedly preparing to launch a major operation to retake Palmyra.
Images distributed by the Observatory, which relies on a broad network on the ground, purported to show residential areas of Palmyra in ruins after months of air strikes.
"Dozens of residents have been killed and hundreds of others wounded" in these strikes, the Observatory said.
An unprecedented truce in Syria, which came into force on February 27, does not apply to IS or the Al-Qaeda-affiliated Al-Nusra Front.
Though the truce has largely held, defying expectations, some violations across frontlines that should have stayed calm have been reported.
Yesterday, an AFP correspondent in an opposition-held area of battered northern city of Aleppo reported air strikes on the Myassar district near Nayrab military airfield, which rebels captured in February 2013.
