A second Russian military jet has violated Turkish airspace in a mission that Nato says “does not look like an accident”.
Russian air strikes have targeted rebel-held areas in northwest Syria for a second day.
The US and Russian military will begin discussions “as soon as possible” to avoid direct clashes in the air above Syria, top diplomats have said.
Russia has begun air strikes against rebel positions within Syria, with the first target near the western city of Homs, US defence officials say.
Four UK jihadists that have gained infamy by fighting or recruiting for the Islamic State will face UN sanctions on the behest of the British government.