Azerbaijan's military says it has shot down an Mi-24 combat helicopter near the breakaway territory of Nagorno-Karabakh and reports said three people were killed, in what Armenia's Defense Ministry called an "unprecedented provocation."
A November 12 statement from the Azerbaijani Defense Ministry said earlier that day, "Two military helicopters, performing combat maneuvers over the Azerbaijani positions, attempted to open fire at the positions of the Azerbaijani armed forces after coming into combat course at 1,700 meters northeast from Kangarli village of Aghdam region."
It said Azerbaijani troops returned fire and brought down the helicopter.
The Azerbaijani Defense Ministry added, "According to preliminary information, the three servicemen of Armenian military forces on board were killed."
It was reportedly the first time a military aircraft has been shot down in the Nagorno-Karabakh region in at least 20 years.
The self-proclaimed "self-defense forces" of Nagorno-Karabakh, a breakaway region controlled by ethnic Armenians, confirmed one of its helicopters was shot down and three people were killed.
Nagorno-Karabakh military spokesman David Babaian said the helicopter was shot down while on a training mission and was not involved in a combat operation.
Nagorno-Karabakh: Why Are They Fighting?
Azerbaijan and Armenia have been at loggerheads for decades over the status of Nagorno-Karabakh, a mountainous region inhabited almost entirely by ethnic Armenians but which is located within Azerbaijan’s internationally recognized borders.
The Soviet government designated the territory an autonomous region within Soviet Azerbaijan in the 1920s. Under Moscow’s iron rule, violence between the Armenians and Azerbaijanis that predated their incorporation into the Soviet Union was kept largely in check.
But as the Soviet Union began to wobble in the late 1980s, simmering tensions boiled over into a six-year war after Nagorno-Karabakh sought to formally join Armenia. The region’s self-styled government declared unilateral independence in 1991, and an estimated 30,000 people died in the conflict before Russia brokered a cease-fire in 1994.
The territory occupies some 4,400 square kilometers of land, and Armenian forces control buffer zones surrounding the breakaway region.
Nagorno-Karabakh has maintained de facto autonomy since the cease-fire, while Azerbaijan maintains its claim to the region.
Internationally mediated negotiations by the Minsk Group co-chaired by France, Russia, and the United States and organized under the Organization for Security and Cooperation in Europe (OSCE) have failed to yield a resolution to the so-called frozen conflict.
Cross-border violence has remained constant in the two decades since the 1994 cease-fire but has not escalated into a full-scale war.
-- Carl Schreck, Luke Johnson
Russia's Interfax news agency said authorities in Nagorno-Karabakh reported that three people aboard the helicopter were killed.
On his Facebook page, Armenian Defense Ministry spokesman Artsrun Hovannisyan called the downing of the helicopter an "unprecedented provocation that leads to an escalation in the situation."
Hovannisyan said Azerbaijani troops were firing on the location where the helicopter crashed.
Hovannisyan called Azerbaijani claims the helicopter attacked Azerbaijani troops "absurd."
"The consequences for the Azerbaijani side will be very painful, and all responsibility will rest with the Azeri political leadership," Hovannisyan wrote.
Hovannisyan told RFE/RL's Armenian Service an investigation of the helicopter wreckage will prove the gunship was not carrying ammunition.
In Brussels, EU foreign-policy chief Federica Mogherini said in a statement that "it is essential that all sides show restraint and avoid any actions or statements which could escalate the situation." Mogherini also called for an inquiry into the incident.
Baku and Yerevan have been locked in a conflict over Azerbaijan's breakaway region of Nagorno-Karabakh for years.
Armenian-backed separatists seized the mainly Armenian-populated region from Azerbaijan during a war in the early 1990s that killed some 30,000 people.
Despite years of internationally brokered talks, the two sides have not yet signed a peace agreement, with Karabakh still internationally recognized as part of Azerbaijan.
Azerbaijani and Armenian forces regularly exchange fire across their frontier and along the Karabakh front line.
An unprecedented spiral of violence this summer -- with more than 20 troops killed from both sides -- raised concerns of a new war, as oil-rich Azerbaijan, which has a large defense budget, said it could take Nagorno Karabakh back by force if diplomacy failed.
The peace talks are being mediated by the OSCE-appointed Minsk Group of mediators and co-chaired by France, Russia, and the United States.
Last month, German Foreign Minister Frank-Walter Steinmeier visited both countries to facilitate a negotiated solution to the conflict.
French President Francois Hollande also hosted the leaders of Armenia and Azerbaijan for talks but the meeting ended without a breakthrough.