The US response to reports of a downed jet remains hard to call, according to Dr H A Hellyer of the Carnegie Endowment for International Peace in Washington.

Speaking to Al Jazeera, Hellyer says the next few hours are likely to be decisive in shaping how the administration reacts.

He says much may depend on whether the pilots are located, and how any such development is handled publicly.

Hellyer warns that if aircrew were captured and then shown on television, it would likely provoke a strong backlash in the US.

In that scenario, he tells Al Jazeera, Donald Trump would be likely to push for a sharper escalation.

Hellyer also says decision-making in Washington is especially difficult to read at present.

He describes US policy as highly centralised around a small number of senior figures, adding that this makes the administration’s next move particularly difficult to predict.