Azerbaijan used tanks to shell the Armenian-held breakaway region of Nagorno-Karabakh on December 9 for the first time since agreeing to a ceasefire 21 years ago, killing one Armenian soldier, the defence ministry of the rebel region said on December 10, according to AFP. "Some 1,500 shots were fired from tanks and grenade launchers," the ministry was quoted as saying.

Deadly skirmishes along the so-called “Line of Contact” are not uncommon, though fighting at the border has so far not escalated into a full-scale military conflict since the 1994 ceasefire that ended a three-year bloody conflict over the area. However, there are worries the region could become the battlefield for a proxy war between Russia and Turkey if the hostilities between the two countries escalate: Armenia is Russia’s closest ally in the region, while Azerbaijan is closely bonded to Turkey.

Azerbaijan’s defence ministry was quoted by Trend news agency as claiming that Armenia had initiated the attack by firing mortar rounds aimed at settlements in Azerbaijan. According to Trend, Armenia fired 86 rounds of mortar and bullets from "high calibre machine guns" on December 9, prompting the Azerbaijani retaliation.

Armenia and Azerbaijan have been in a state of frozen conflict since that 1994 ceasefire; a peace accord was never signed. While the wealthier Azerbaijan has invested much more in its military, reportedly purchasing $4bn worth of armaments from Russia, since 2013, destitute Armenia enjoys Russia's financial and defence support, which has prevented Azerbaijan from reinitiating open conflict to recover Nagorno-Karabakh and the seven surrounding regions that are under Armenian occupation.

Nagorno-Karabakh declared its independence in 1991, but no sovereign state has recognised it – not even Armenia. Meanwhile, the UN deems the breakaway area as Azerabijani territory. Peace negotiations between Armenia and Azerbaijan, which are overseen by a special group within the Organisation for Security and Cooperation in Europe (OSCE) called the Minsk Group, have made no progress in over two decades.

A meeting between the Azerbaijani and Armenian presidents, which was expected to take place on December 1 in Paris, was postponed indefinitely, as the two leaders of state reportedly avoided each other at the UN climate change conference COP21.

According to Richard Giragosian, director of Yerevan-based Regional Studies Centre, the escalation of violence at the border between Azerbaijan and Nagorno-Karabakh and Azerbaijan and Armenia signals Baku's frustration with the stalemate in negotiations. Since the summer of 2014, violent border clashes have become more common, and Azerbaijani media reports on Armenian ceasefire violations almost on a daily basis. While Giragosian doubts that there is enough political will in Baku to restart a full-fledged war, the violence at the border raises the risk of a war by accident "based on miscalculation and overreaction on both sides".

The issue of Nagorno-Karabakh is used as a political tool in both Armenia and Azerbaijan, to create a sense of imminent conflict and thus distract the population from domestic political failings, and to galvanise the electorate's support for the ruling parties. Both the Armenian and Azerbaijani administrations have significant shortcomings in the areas of corruption and human rights.

For Armenia, the conflict has had tangible negative effects on its economy, for its borders with Azerbaijan and Turkey, a long-standing ally of Azerbaijan's, have been closed for over two decades, hampering the impoverished country's trade and pushing it further into Russia's arms. 

Meanwhile, an escalation of the conflict could draw in regional powers like Russia and Iran in support of Armenia, and Turkey and potentially Israel in support of Azerbaijan. Turkey and Russia have been at odds ever since Turkey downed a Russian Su-24 bomber on November 24, so the conflict over Nagorno-Karabakh could become a proxy war between the two regional powers, much what is starting to happen in the civil war in Syria.