Analysis by Emre Temel, BBC Turkish (English)

Diplomatic relations between Turkey and Azerbaijan have always been strong. When fighting erupted over Nagorno-Karabakh on Sunday, Turkey immediately extended its support "both on the field and at the negotiation table", in the words of its foreign minister.

They share a similar history, language and heritage and their leaders often refer to "one nation and two states". Turkey's border with Armenia has been closed since 1993 as a gesture of support over Nagorno-Karabakh.

President Erdogan has vowed to stand by Azerbaijan "with all its resources and heart". But it's still unknown whether Turkey has supplied Azerbaijan with military experts, drones and warplanes, as Armenia alleges.

And yet it is Russia, not Turkey, that holds the key to the region. Russia has a mutual defence pact with Armenia and a military base there. Turkey is already at odds with Russia over Syria and Libya, and the Caucasus could open a new front.

Standing up to Russia would be too risky for Turkey economically and militarily. Russia is Turkey's prime energy supplier and a key trading partner.

https://www.bbc.com/news/world-europe-54345622