Two US fighter jets fired warning flares on Wednesday after two Russian jets entered an agreed de-confliction zone over Syria.

The two US F-22 fighter aircraft fired warning flares after the Russian Su-25 jets entered the de-confliction area in airspace east of the Euphrates river in Syria, the US military said.

The Russian jets left the area after the flares were fired, an American official told Reuters on condition of anonymity.

Politically, the eighth round of the Geneva talks ended on Thursday in what United Nations special envoy Staffan de Mistura called a “missed opportunity” after the regime refused to hold direct negotiations with the opposition.

Syrian regime negotiator Bashar al-Jaafari said that de Mistura’s call on Russian President Vladimir Putin to exert pressure on Damascus hampered his mission as a mediator.

He also accused the opposition of sabotaging the Geneva talks.

Jaafari said Damascus did not want the talks to fail but the opposition had put down a precondition with a declaration that Assad had no role in Syria’s political transition.

Opposition spokesman Yehya al-Aridi told Asharq Al-Awsat that Jaafari cannot declare the end of the Geneva talks or the Riyadh 2 declaration.

“From now on, there should be greater solidarity in Geneva in confronting the arrogance of the regime and its defiance of international law and the UN,” he added.