President Bashar al-Assad on Monday described the deadly US-led coalition raid on his forces in eastern Syria at the weekend as "flagrant American aggression".
Speaking to Iran's deputy foreign minister Hossein Jaberi Ansari, Assad accused world powers of supporting "terrorist organisations" in Syria like the Islamic State jihadist group.
"Every time the Syrian state makes tangible progress either on the ground or towards national reconciliation, anti-Syrian states increase their support of terrorist organisations," Assad said in comments published by state news agency SANA.
"The latest example of this is the flagrant American aggression on one of the Syrian army's positions in Deir Ezzor to the benefit of Daesh" on Saturday, he added, using the Arabic acronym for IS.
The US-led raid on Saturday evening hit a Syrian army post near the eastern city of Deir Ezzor, where government forces have been fighting off IS jihadists since last year.
At least 62 Syrian soldiers were killed in the strike. The Pentagon admitted it may have hit Syrian troops but said it had been tracking an IS position there.
"Anti-Syrian forces are expending all their energy and capabilities to prolong the terrorist war against Syria," Assad said.
The Syrian government has accused the US-led coalition -- which has been bombing IS in Syria for more than two years -- of carrying out an "intentional" strike to support IS in the area.
In a phone interview from Damascus on Sunday, senior Assad adviser Buthaina Shaaban told AFP that the government "believes that the strike was intentional".
"None of the facts on the ground show that what happened was a mistake or a coincidence," she said.