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.
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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 of 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 in the Jabal Tharda area of Deir Az Zor.
The Observatory said on Sunday the plane came down in the same area, which overlooks the government's Deir Az Zor military airport.
The city's airport and some government-held districts have been entirely surrounded by ISIL since last year, with the airport providing the only external access.
Heavy air strikes over the past 24 hours have hit ISIL-controlled areas near Deir Az Zor city, according to the Observatory and Syrian state media.
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Source: News Agencies