"Today, at 17:00, two US Air Force F-16 planes, two A-10 planes and an unmanned combat aerial vehicle carried out airstrikes on key Syrian army defense positions around six kilometers [3.7 miles] south of the Deir ez-Zor airport," reconciliation center head Vladimir Savchenko said.
The Russian operation commander contacted the Combined Joint Operations Center in Qatar after being notified by the Syrian side about the attack, he added, noting that the strikes then ended at 17:50.
"After the strikes, Islamic States fighters started an offensive in the area. Heavy fighting continues. From 19:00, Russian Aerospace Forces planes are supporting Syrian army units by striking IS targets. A total of 10 strikes have been carried," he said.
Syria has been mired in civil war since 2011, with government forces fighting numerous opposition factions and extremist groups, including the IS, which is outlawed in many countries, including Russia. The government-held city of Deir Ez-Zor has been under siege from IS since July 2014.
The US-led coalition has been carrying out anti-IS strikes since September 2014 without Syrian government consent.