So far, we have not heard the reason for the crash of our attack aircraft from the Defense Ministry. We know for sure that the aircraft was in Syrian airspace, over the territory of Syria," Dmitry Peskov, Vladimir Putin's spokesman, told Russian agencies.

"It would be wrong to make some kind of assumptions right now, to make any statements until we have the complete picture. Therefore, we just have to be patient. This is a very serious incident, but again, it is impossible to say anything without complete information."

Mr Peskov said Mr Putin would likely "touch on" the subject during a meeting with King Abdullah of Jordan today, and would be "some kind of reaction" later in the day.