ISIL fighters shot down a Syrian military plane in the eastern Syrian city of Deir Az Zor, the group's Amaq news agency reported on Sunday.
"A Syrian warplane belonging to the Syrian regime was brought down when targeted by fighters from the Islamic State in the city of Deir al-Zor," Amaq said in an online statement.
The UK-based Syrian Observatory for Human Rights, which monitors the Syrian conflict now in its sixth year, said the pilot of the MIG Syrian warplane was killed.
Earlier in the day, Syrian state news agency SANA reported that government troops had regained territory in the eastern province lost to fighters affiliated with the Islamic State in Iraq and the Levant (ISIL, also known as ISIS) "as a result of the American aircraft aggression."
The US military said it may have unintentionally struck Syrian troops while carrying out a raid against ISIL in Deir Az Zor on Saturday.
Russia's military said it was told by the Syrian army that at least 62 soldiers were killed and more than 100 wounded in the raid.