Moscow has warned the US that if militias it supports in northeast Syria again attack positions of pro-government forces backed by Russia, the Russian military will use all its force to retaliate.

The troops of the Syrian Democratic Force (SDF), a predominantly Kurdish militia that receives support from the US military, have twice attacked positions of the Syrian Arab Army in the Deir ez-Zor governorate with mortar and rocket fire, according to the Russian Defense Ministry's spokesman, Major General Igor Konashenkov.

“Russia unequivocally told the commanders of US forces in Al Udeid Airbase (Qatar) that it will not tolerate any shelling from the areas where the SDF are stationed,” Konashenkov said, adding that the attacks put at risk Russian military advisers embedded with Syrian government troops.

“Fire from positions in regions [controlled by the SDF] will be suppressed by all means necessary,” he stressed.

Konashenkov said Moscow suspected the SDF of colluding with the terrorist group Islamic State (IS, also known as ISIS/ISIL) in Deir ez-Zor rather than fighting it, as it claims to be. He said Russia had detected the transfer of SDF fighters from the IS stronghold of Raqqa, to join forces with the jihadists.

“SDF militants work to the same objectives as IS terrorists. Russian drones and intelligence have not recorded any confrontations between IS and the ‘third force,’ the SDF,” the Russian general said.

READ MORE: Syrian troops cross Euphrates as they advance east of Deir ez-Zor (VIDEO)

The statement said that the siege of Raqqa by the SDF has been halted, apparently in response to the latest advances by Syrian government forces in Deir ez-Zor, which is located to the east from Raqqa along the Euphrates River.

“The central parts of the former ISIL capital, which account for roughly 25 percent of the city, remain under full control of the terrorists,” Konashenkov remarked.

According to the statement, in the last 24 hours Syrian government troops “continued their offensive operation” to destroy the last “IS bridgehead” near the city of Deir ez-Zor, the provincial capital. Troops led by Syrian Army General Suheil al-Hassan liberated around 16 sq km of territory and two settlements on the western bank of the Euphrates River.

“More than 85 percent of Deir ez-Zor's territory is under the full control of Syrian troops. Over the next week the city will be liberated completely,” Konashenkov said.

The city of Deir ez-Zor in eastern Syria was besieged by Islamic State in 2014. Syrian government forces lifted the blockade of the city in early September.

However, the liberation of Deir ez-Zor also triggered a confrontation between Syrian government forces and the US-backed SDF militants, the point of contention being control of Deir ez-Zor’s oil fields.

Following Damascus’s strategic victory, food, medicine and other essentials started to reach the city by convoy, where previously the inhabitants had to rely on air-drops.

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The escalation of tension in eastern Syria is mirrored in the western Idlib governorate, where militant forces this week attacked Syrian positions in a designated de-escalation zone. The offensive threatened a unit of Russian military police, who were stationed in the area to monitor the ceasefire. Russia mounted an emergency rescue operation on Wednesday, in which three Russian special operations troops were injured. The Russian Defense Ministry claimed that the militants’ offensive had been instigated by US special services.