Fifteen soldiers died Sunday in an ISIS attack on an army bus in the central Syrian desert, a war monitor said.

State news agency SANA had reported 13 dead “including officers” and 18 wounded.

ISIS cells “attacked a military bus” in the Palmyra desert, “killing 15 soldiers and wounding 18 others,” the British-based Syrian Observatory for Human Rights said.

The death toll could rise as most of the soldiers were “seriously wounded,” said the Observatory, which relies on a network of sources across the country.

ISIS did not immediately claim responsibility for the attack.

The Observatory said 61 pro-regime soldiers and Iran-affiliated militiamen had been killed in ISIS attacks in the desert of Syria since the start of the year.

Despite the group’s territorial defeat in 2019, ISIS continues to launch deadly attacks from hideouts in the Syrian desert, which extends from the outskirts of the capital Damascus to the Iraqi border.

In early January, nine Syrian soldiers and allied fighters were killed in a similar attack on a military convoy in Syria’s east.

On January 20, ISIS fighters launched their biggest assault in years, attacking a prison in the Kurdish-controlled northeast Syrian city of Hasaka, aiming to free fellow extremists.

Almost a week of intense fighting left more than 370 dead, according to the Observatory.

ISIS leader Abu Ibrahim al-Hashimi al-Qurashi blew himself up in early February during a raid by US forces on his house in Syria’s northwest region of Idlib, Syria’s last major opposition bastion.

About half a million people have died and millions have been displaced since the Syrian conflict erupted in 2011, after nationwide protests against the government were met with a brutal crackdown.

It escalated into a devastating war that drew in regional and international powers.