The US military has backed up Turkey's claim that Turkish pilots warned a Russian jet 10 times - but failed to get a response - before shooting it down.
"We were able to hear everything that was going on, these (communications) were on open channels," Baghdad-based military spokesman Colonel Steve Warren said in a video call with reporters.
Asked if he could confirm reports 10 warnings were issued by Turkish pilots without response, Warren said: "I can confirm that, yes."
He added it was not immediately clear on which side of the Turkish-Syrian border the Russian jet had been flying, and it would take some time to analyse data before arriving at that determination.
Another US official, however, said the US believes Russia's incursion into Turkish airspace likely lasted only a matter of seconds before Turkey shot down the warplane.
The official spoke on condition of anonymity and told Reuters that assessment was based on preliminary indications.
The Pentagon says no US forces were involved in the Turkish downing of the Russian jet.
The United States has a strong presence in Turkey and regularly flies warplanes out of the air base in Incirlik as it conducts bombing runs against Islamic State targets in Syria and Iraq.
Pentagon officials have previously condemned the actions and tactics of Russian pilots after Russian jets violated Turkish airspace last month.
In Tuesday's incident, the Turkish army said the plane was shot down by two Turkish F-16s after violating Turkish airspace 10 times within a five-minute period.
Russia insists the jet was inside Syrian airspace and condemned the downing as "a very serious incident".
The US believes Russia's incursion into Turkish airspace on Tuesday likely lasted only a matter of seconds before Turkey shot down the warplane, a US official who spoke on condition of anonymity told Reuters.
They said that assessment was based on preliminary indications.