U.S.-backed forces in eastern Syria say Russia bombed their positions on Monday in a major natural gas field they recently captured from Islamic State militants.
The Syrian Democratic Forces said a Russian airstrike killed one of its fighters and wounded two others in the Conoco gas field, in Deir el-Zour province. Russia's Defense Ministry denied the report.
SDF fighters captured Conoco field, Syria's largest, from IS militants on Saturday.
The SDF issued a statement later Monday saying that its forces retaliated by shelling the source of fire and positions of "hostile forces."
It was not the first time the SDF has accused Russia of targeting its forces in oil and gas-rich Deir el-Zour, where Russian backed Syrian troops are waging a separate offensive against the extremists. The two sides are racing to defeat the militants and snap up oil and gas fields, fueling fears of conflict between the two groups and their superpower sponsors.
Both the U.S. and Russia have embedded special forces with their respective partners and are supporting their advances with aggressive air strikes.
The Pentagon accused Russian jets of attacking the SDF last week. Russia in turn said its forces were targeted twice from SDF-held territory.
SDF fighters have been making their way down the east bank of the Euphrates River in Deir el-Zour, while Syrian troops are mainly operating on the western bank. Last week, Syrian troops along with allied Shiite militias from across the region crossed into parts of the east bank, where they ran into fierce resistance from IS militants entrenched there.
"They are losing fighters wholesale," said Germany-based Deir el-Zour native Omar Abu Layla, who is monitoring the battles through local contacts.
The Britain-based Syrian Observatory for Human Rights says 72 pro-government fighters have been killed in battle with the jihadists since crossing the Euphrates last week. At least seven Russian soldiers have been killed, and Russia's Defense Ministry acknowledged that one of its generals was killed in the area on Sunday.
Syria's largest oil field, the al-Omar, is located on the eastern side of the river.
Elsewhere in Syria, Russian and government warplanes stepped up their airstrikes against rebels as well as al-Qaida-linked insurgents in different areas, straining a patchwork of cease-fires and "de-escalation" agreements that had brought relative calm in recent weeks.
Activists and monitoring groups reported airstrikes in Aleppo, Idlib and Hama provinces, as well as clashes between rebels and pro-government forces in northern Syria and on the outskirts of the capital, Damascus.
The Observatory said the airstrikes killed 37 in the town of Jisr al-Shughour and nearby areas in Idlib province. The Syrian Civil Defense, also known as the White Helmets, which is active in opposition-held areas, said 15 people were killed and 30 wounded in Jisr al-Shughour alone, adding that other people were killed in other areas in the province.
Two people were killed Monday in shelling on President Bashar Assad's ancestral village of Qardaha, state media reported. Syria's state broadcaster said the village has been shelled by "terrorists" for two days straight. It says two people were wounded Sunday.
Qardaha is located in the coastal mountains of northwest Syria. Assad's father, the late president Hafez Assad, was born in Qardaha. He was buried there in 2000.
The village has been largely spared from Syria's civil war, which grew out of demonstrations in 2011 against the Assad family's four-decade rule.
The Observatory also reported the shelling, saying two civilians were killed.
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