BEIRUT -- Syrian government warplanes and special forces on Sunday destroyed several positions of the Islamic State group in the eastern province of Deir el-Zour.  The advance regained territory lost to the terrorists Saturday when Syrian troops were hit with airstrikes by the U.S.-led coalition. 

The U.S. military has admitted that it may have unintentionally struck Syrian troops while carrying out a raid against IS on Saturday.  The incident has threatened an already-fragile U.S. and Russian-brokered cease-fire that has largely held despite dozens of alleged violations on both sides. 

The Syrian Foreign Ministry called the coalition airstrikes a "dangerous and blatant aggression against the Syrian Arab Republic and its army." 

The ministry's statement, sent to the presidents of the United Nations and the U.N. Security Council, said American warplanes repeatedly attacked Syrian army positions on Saturday afternoon.  It said the airstrikes were "on purpose and planned in advance," and killed dozens of Syrian soldiers. 

Russia's military said it was told by the Syrian army that at least 62 soldiers were killed in the Deir el-Zour air raid and more than 100 wounded. 

On Sunday, the state-run SANA news agency quoted an unnamed military official as saying that dozens of IS fighters were killed in the offensive on Tharda mountain under the cover of Syrian airstrikes.  IS had claimed that its fighters captured Tharda mountain, which overlooks the city's government-controlled airport. 

The Syrian military official said government troops had regained control of areas the terrorists captured, "as a result of the American aircraft aggression." 

Meanwhile, the Britain-based Syrian Observatory for Human Rights said IS fighters shot down a Syrian Russian-made MiG warplane over Tharda mountain, adding that its pilot was killed.  The Observatory reported that intense airstrikes by Russian warplanes have killed at least 38 IS fighters since Saturday. 

The Syrian military said the deadly coalition airstrike hit a base in Deir el-Zour that was surrounded by IS, allowing the terrorists to advance and overrun Syrian army positions in the area. 

Tens of thousands of people live in government-held neighborhoods of Deir el-Zour under the siege of IS fighters.  Government areas have been relying on aid that was being dropped from aircraft. 

IS controls much of the province that carries the same name and borders Iraq. 

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Associated Press writers Albert Aji in Damascus, Syria and Maamoun Youssef in Cairo contributed to this report. 

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