The two neighbours in the South Caucasus are locked in conflict over Nagorno-Karabakh, a region of Azerbaijan under the control of ethnic Armenian forces backed by Armenia.
At least 11 troops and a civilian have been killed during border clashes between Azerbaijan and Armenia that have continued for three days despite international calls for restraint.
The international community worries about clashes between Armenia and Azerbaijan in part because of the threat to instability in the South Caucasus, a region that serves as a corridor for pipelines taking oil and gas to world markets.
The fighting between the arch-foes in the South Caucasus since Sunday is the heaviest in years, raising fears of a major flare-up in the volatile region.
Azerbaijan said seven of its troops – including a major general and a colonel – and a civilian had died on Tuesday, and Armenia said four of its troops had been killed, its first reported fatalities in the clashes.
Overall, 16 people have been killed from both sides since Sunday.
Azerbaijan and Armenia both said exchanges of fire that began on Sunday had continued into Tuesday and each accused the other of ceasefire violations and shelling.
Locked in conflict
The two neighbours in the South Caucasus have been locked in conflict over Nagorno-Karabakh, a region of Azerbaijan that has been under the control of ethnic Armenian forces backed by Armenia, who declared independence during a conflict that broke out as the Soviet Union crumbled in 1991. International efforts to settle the conflict have stalled.
The latest clashes occurred some 300 kilometres from the mountainous enclave.
Though a ceasefire was agreed upon in 1994, Azerbaijan and Armenia continue to accuse each other of shooting attacks around Nagorno-Karabakh and along the separate Azeri-Armenian frontier.
Armenian and Azerbaijani forces have frequently engaged in clashes. In 2016, scores were killed in four days of fighting.
READ MORE: Reasons for fighting in Karabakh between Azerbaijan, Armenia
Fighting in Tavush
The latest incident began on Sunday when Armenian and Azerbaijani troops exchanged fire in the northern section of their border. Officials in both countries blamed each other for starting the fighting and said that sporadic shelling continued Monday.
Azerbaijani President Ilhan Aliyev denounced what he described as “another provocation of Armenia” and vowed to protect Azerbaijan's national territory.
Armenian Prime Minister Nikol Pashinyan also accused Azerbaijan of provoking the clashes and warned that it would "bear responsibility for the unpredictable consequences".
Meanwhile, Russia urged both countries to show restraint after the escalation in deadly fighting along their shared border.
"We are deeply concerned about the exchange of fire on the Armenian-Azerbaijani border," Kremlin spokesman Dmitry Peskov told reporters, adding that Moscow was calling on "both sides to show restraint".
Peskov told reporters that Russia was "ready to provide mediation efforts as a co-chair of the Minsk Group" after the latest flare-up.
Russia has maintained close ties with both Armenia and Azerbaijan.
NATO called on Azerbaijan and Armenia to take all necessary measures to prevent further escalation, according to James Appathurai, the US-led alliance's special representative for the Caucasus and Central Asia.
Toivo Klaar, the EU's special representative for the South Caucasus, voiced concern about the exchange of fire on the Armenia-Azerbaijan border, tweeting that it's "important for both countries to show restraint and to use all channels of communication, both direct and the good offices of the OSCE Minsk Group Co-Chairs".
Very concerned about exchange of fire on Armenia-Azerbaijan border. Important for both countries to show restraint and to use all channels of communication, both direct and the good offices of the #OSCE Minsk Group Co-Chairs— Toivo Klaar (@ToivoKlaar) July 13, 2020
Turkey, which has close ethnic and cultural ties with Azerbaijan, voiced strong support to Baku in the conflict.
“What Armenia did is unacceptable. It must get back to its senses,” Turkish Foreign Minister Mevlut Cavusoglu said in an interview with state broadcaster TRT.
“Azerbaijan is not alone. The Turkish Republic and the Turkish people, is with Azerbaijan with all of its capabilities.”
Turkey's President Erdogan said that the attack carried out on the borders of the two states with heavy weapons shows that it was a deliberate attack on Azerbaijan.
"This attack goes beyond the diametre of Armenia. The aim is both to block the solution in the Upper Karabakh and to reveal new conflict areas."
The US condemned the violence. “We urge the sides to stop using force immediately, use the existing direct communication links between them to avoid further escalation, and strictly adhere to the ceasefire,” said State Department spokesperson Morgan Ortagus in a statement.
Mediated by the "Minsk Group" of diplomats from France, Russia and the United States, peace talks between the two sides have been going on since the 1994 ceasefire.
Aliyev threatened last week to withdraw from talks "if they do not yield results" and rejected statements by negotiators that there could be no military solution.
Despite the strong wording, his remarks were widely seen as diplomatic pressure for the stalled talks' intensification.
Armenia, which controls the disputed region, is happy with the status quo in Karabakh that also suits Russia's interests as the Kremlin uses its power-broker's role in asserting its influence in the ex-Soviet republics.
Desperate to restore its territorial integrity by diplomatic means, energy-rich Azerbaijan, whose military spending exceeds Armenia's entire state budget, has repeatedly threatened to take back the territory by force.
READ MORE: Azerbaijanis displaced by the Karabakh conflict wish to return home