Nagorno Karabakh - Troops are "always ready to war", says a commander of a military unit stationed in the Martuni area of the contested Nagorno Karabakh, a landlocked region in the southern Caucuses that formerly made up the outer edges of the Soviet Union.

For more than two decades, the autonomous region has been controlled by Armenian-backed separatists. But it is internationally recognised as the territory of Armenia's neighbour, Azerbaijan.

The war in Karabakh is silent, cold and dirty.

It flared up in April 2016 when an all-out war erupted between the two factions. More than 400 people died on each side.

WATCH: What triggered the conflict?

Nagorno-Karabakh has been in dispute since the collapse of the Soviet Union in 1991.

After that, separatists backed by Yerevan announced allegiance to Armenia and then declared an independent republic, a move that has not been recognised elsewhere, including by Armenia.

In the subsequent fighting, about 30,000 people were killed, and thousands of others from both ethnic groups fled their homes.

A ceasefire brokered by Russia was signed in 1994, but the two countries have never agreed on a lasting peace.