Azerbaijan fighting against Armenian occupation of Karabakh region, which lies inside Azerbaijani territory according to Soviet constitution
The region of Karabakh, which is internationally recognised as officially belonging to Azerbaijan, has been occupied by ethnic Armenians since a separatist movement took over the region in 1994 after three years of bloody clashes.
About 150,000 people are thought to live in the region, which has an area of around 12,000 square kilometres (4,400 square miles).
The causes of the recent deadly clashes between Armenians and Azerbaijanis in Karabakh are rooted in an intractable dispute concerning the status quo of the Karabakh region following World War I. This led to a short war between Azerbaijan and Armenia for the region between March and April in 1920.
After Azerbaijan and Armenia were subsumed into the Soviet Union, the Nagorno-Karabakh Autonomous Region was established within Azerbaijan by the Soviet Union in 1924. Following this, violent conflict had not reemerged till the end of the Soviet era.
During the dissolution of the Soviet Union in the late 1980s, the question of the future of the region became a source of emnity once again and clashes began between ethnic Azerbaijanis and Armenians in November 1988. The clashes continued on and off until both countries earned their own indepedencies in 1991.
Karabakh held a referendum in December 1991 in order to create an independent state, which would mean unilaterally declaring itself as separate from the Republic of Azerbaijan . The majority of those who went to the referendum polls voted in favour of independence however most of the Azerbaijanis living in Karabakh was boycotted it, with the reason that referandum was illegitimate.
Most countries do not recognise the legitimacy of Karabakh's declaration of independence. This is partly because only 15 republics of the Soviet Union could declare independence from the union according to the Soviet constitution and Karabakh was not a republic. Another reason is because unilateral declarations of independence are often rejected because they violate international law.
Following the referendum, the conflict escalated between the countries, resulting in at least 30,000 casualties and displacing an estimated 1 million people from both sides by the end of a full-scale war in 1993.
Azerbaijan and Armenia reached an unofficial ceasefire in May 1994 through Russian mediation. During the conflict, the Russians reportedly supported the Armenian forces militarily and politically.
The Russian-sponsored ceasefire survives to this day, though clashes like the ones that took place this week break out from time to time.
The Karabakh region has recently seen heavy fighting after Armenian and Azerbaijani military forces clashed with each other along the front lines on April 2, leading to numerous deaths of Azerbaijanis and Armenians.
The clashes have prompted the major powers to invoke the 1994 ceasefire agreement, calling on both sides to end the fighting in order to prevent the destabilisation of the turbulent South Caucasus.
Both sides have reported significant casualties, accusing each other of violating the ceasefire in what appears to have been the fiercest clashes since the 1990's.
Last year, five Armenian soldiers were killed and eight wounded after border guards from both countries exchanged fire on Aug. 22.
There were border clashes between the countries in 2014. Thirteen Azerbaijani soldiers were reportedly killed during skirmishes which took place between July 30 and Aug 2 in 2014.