By Andrew Osborn
MOSCOW (Reuters) - Russia said on Thursday it had warned the United States it would target areas in Syria where U.S. special forces and U.S.-backed militia were operating if its own forces came under fire from them, something it said had already happened twice.
Russia was referring to the Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab militias fighting with the U.S.-led coalition, which Moscow said had diverted from the battle to take Raqqa to Deir al-Zor, where Russian special forces are helping the Syrian army push out Islamic State militants.
The Russian Defence Ministry said the SDF had taken up positions on the eastern banks of the Euphrates with U.S. special forces, and had twice opened fire with mortars and artillery on Syrian troops who were working alongside Russian special forces.
"A representative of the U.S. military command in Al Udeid (the U.S. operations center in Qatar) was told in no uncertain terms that any attempts to open fire from areas where SDF fighters are located would be quickly shut down," Major-General Igor Konashenkov said in a statement.
"Fire points in those areas will be immediately suppressed with all military means."
In Deir al-Zor province of eastern Syria, Islamic State is battling two separate offensives, launched by the SDF on one side and the Syrian army and its allies on the other.
The Syrian army, backed by Russian and Syrian war planes, has captured about 100 km (160 miles) of the west bank of the Euphrates this month, reaching the Raqqa provincial border on Wednesday, the Syrian Observatory for Human Rights reported.
Syrian troops also crossed to the eastern side of the river on Monday. The SDF's advances have been on the eastern bank of the river.
The convergence of the two rival offensives has increased tensions in Deir al-Zor. The U.S.-backed militia said on Saturday they had come under attack from Russian jets and Syrian government forces, something Moscow denied.
The SDF warned on Monday against any further Syrian army advances on the eastern riverbank.
On Tuesday Russia's Defence Ministry said the waters of the Euphrates had risen as soon as the Syrian army began crossing it, suggesting this could only have happened if upstream dams held by the U.S.-backed opposition had been opened.
Konashenkov, in his Thursday statement, questioned the nature of SDF's relationship with Islamic State (IS). Russian drones did not detect any clashes between the two groups when SDF fighters approached Deir al-Zor, he said.
(Editing by Gareth Jones)