An attack by jihadis with the Islamic State group on Syrian government forces in the war-torn country's east has killed 33 soldiers, a monitor said Saturday, revising an earlier toll of 26 deaths.
The attack late Thursday on an army bus was the extremist group's deadliest targeting on government forces this year, according to the Syrian Observatory for Human Rights.
Despite losing the last territory they controlled in Syria in 2019, IS has maintained hideouts in the vast Syrian desert from which it has carried out ambushes and hit-and-run attacks.
"The death toll from the army bus attack rose to 33 soldiers," said Rami Abdel Rahman, who heads the Britain-based monitoring group which relies on a wide network of sources inside Syria.
The jihadis surrounded the bus in the desert near Mayadeen, in Deir Ezzor province, and opened fire, the Observatory reported Friday.
IS later claimed the attack, saying its fighters had carried out an ambush "on two military buses," targeting them "with heavy weapons and rocket-propelled grenades" and setting one on fire, according to a statement from the jihadis' Amaq news agency.
Syrian state news agency SANA issued a statement late Saturday from the foreign ministry accusing "the American occupation forces and their terrorist organizations" of targeting the bus.
"This criminal and terrorist aggression" comes "in the context of the support and sponsorship of the United States of America for terrorist organizations, at the forefront of which is Daesh," it said, using the Arabic acronym for IS.
Abdel Rahman told AFP the jihadis were trying to show that IS "is still active and powerful despite the targeting of its leaders."
Last week, IS announced the death of its leader Abu al-Hussein al-Husseini al-Qurashi, who it said was killed in clashes in northwestern Syria, and named a successor.
IS members in recent weeks have increased their attacks in the north and northeast.
Earlier this week, 10 Syrian soldiers and pro-government fighters were killed in an IS attack in the former jihadi stronghold of Raqa province, the Observatory said.
Syria's war broke out after President Bashar al-Assad's government crushed peaceful protests in 2011. It has since drawn in foreign powers and global jihadis.
The conflict has killed more than half a million people and driven half of the country's pre-war population from their homes.