Describing the incident as 'very serious', Moscow insists the aircraft was flying over Syria.
Turkish Presidential sources say that the Russian military bomber was shot down by the Turkish military.
This is the first time a NATO member's armed forces have shot down a Russian or Soviet military aircraft since the 1950s, and NATO have now called an extraordinary meeting for this evening.
This comes against a backdrop of escalating fears worldwide over terrorism, with the US taking the rare step of issuing a worldwide travel alert for Americans.
The warnings are focused on the transport system as millions of Americans prepare to travel ahead of thanksgiving on Thursday.
Transport Police Chief Polly Hanson says security is being stepped up at airports and train stations.
Meanwhile, French President Francois Hollande is meeting with President Obama in Washington today to discuss support for its newly declared war on Islamic State.
Police hunting Paris terror suspect Salah Abdeslam have recovered a suspected suicide belt – dumped in a rubbish bin, and Brussels remains on high alert, amid fears of an imminent attack.
