BAKU/YEREVAN -- Armenia said a Turkish F-16 fighter jet shot down one of its warplanes, as fighting intensified near the long-disputed Nagorno-Karabakh region and fears grew of an outbreak of a new, full-scale war between Armenia and Azerbaijan.
Both Ankara and Baku called Yerevan’s claim about the warplane’s downing on September 29 "absolutely untrue,” which came on the third day of a major flare-up of the decades-old conflict.
The fighting is some of the worst the region has seen in years.
Amid international calls for an end to the hostilities, the UN Security Council scheduled an emergency meeting to discuss the fighting, which has threatened to draw in Russia and regional power Turkey, a close ally of Azerbaijan.
An Armenian Defense Ministry spokeswoman said in a statement that a Sukhoi Su-25 flown by Armenia’s air force had been on a military assignment in Armenian airspace when it was downed by an F-16 jet owned by the Turkish air force. Much of NATO member Turkey's air power is U.S.-made.
In Azerbaijan, a Defense Ministry spokesman denied the claim, as did Fahrettin Altun, a spokesman for Turkey's presidency, calling it “absolutely untrue."
"Armenia should withdraw from the territories under its occupation instead of resorting to cheap propaganda tricks," Altun said.
Turkey is Azerbaijan’s closest ally, and stalwart adversary of Armenia, and there are growing fears that Ankara could seek to intervene on behalf on Baku.
Both Armenia and Azerbaijan have fielded helicopters, drones, tanks, and artillery already -- a considerable escalation of past skirmishes and low-level shooting.
Turkey "will be fully committed to helping Azerbaijan take back its occupied lands and to defending their rights and interests under international law,”Atlun said.
Azerbaijan and Armenia have been locked in conflict over Nagorno-Karabakh since the waning years of the Soviet Union.
The two sides fought a war from 1988-94 that claimed the lives of more than 30,000 people and ended in an uneasy cease-fire.
Since then, the region has been under the control of ethnic Armenian forces. The region's 1991 declaration of independence has not been recognized, though Armenia, which is its sole outlet to the outside world, has hosted official representative offices of the region's administration.
While the conflict is generally considered to be "frozen," sporadic violence has broken out over the years, and internationally mediated negotiations have failed to achieve a resolution.
It wasn’t immediately clear what caused the long-simmering conflict to erupt anew on September 27.
The clashes are the heaviest since at least 2016 and have reignited concern over stability in the South Caucasus, a corridor for pipelines carrying oil and gas to world markets.
Earlier on September 29, dozens of deaths were reported. Azerbaijan’s Defense Ministry said the Armenian military shelled the Dashkesan region -- an accusation rejected by Yerevan as “absolutely false.”
"On the night of September 28-29, intense battles continued along the entire front line," Azerbaijan’s Defense Ministry said in a statement, referring to the so-called Line of Contact that separates Armenian and Azerbaijani forces.
The Armenian Defense Ministry added that "battles with varying intensity continue."
Calls For Calm
The violence has drawn calls by Russia and Western governments seeking to keep it from spiraling into outright war.
Kremlin spokesman Dmitry Peskov said the situation was “a cause for concern for Moscow and other countries.”
“We believe that the hostilities should be immediately ended," Peskov said.
Russia is among the largest supplier of weaponry to both Azerbaijan and Armenia. It also has a military base in Armenia.
During a visit to Greece, U.S. Secretary of State Mike Pompeo called on both sides to stop the violence and work with the Minsk Group of the Organization for Security and Cooperation in Europe (OSCE) to "return to substantive negotiations as quickly as possible."
That call was echoed later by the U.S. envoy to the Vienna-based security organization, whose so-called Minsk Group is headed by Russia, the United States, and France.
WATCH: Turkish-Russian Rivalry Influences Azerbaijan-Armenia Fighting
"We call on the sides to stop fighting immediately and return to the negotiating table as soon as possible and without preconditions," Ambassador James Gilmore said in a statement.
German Chancellor Angela Merkel held phone calls with the leaders of both Armenia and Azerbaijan, according to her spokesman. That came on the heels of a joint statement by the foreign ministers of Britain and Canada, who expressed concern over the “large-scale military action.”UN Secretary-General Antonio Guterres has called directly on Armenia and Azerbaijan to immediately halt hostilities. Guterres who spoke to both Azerbaijan's President Ilham Aliyev and Armenian Prime Minister Nikol Pashinian, also called on the sides to accept the deployment of monitors from the OSCE.
Aliyev flatly ruled out any possibility of talks in a statement on Russia's state TV channel Rossia 1. Pashinian said talks could not take place while fighting continued.
Late on September 28, separatists fighters in Nagorno-Karabakh reported that 26 Armenian servicemen had been killed in the latest fighting, bringing its total losses to 84.
Azerbaijan said 10 civilians have been killed and some 30 wounded.
Armenian reports that they have killed Azerbaijani forces have not been confirmed by Baku.
On September 27, Armenia declared martial law and a total mobilization of men in response to attacks on the enclave, including in the regional capital of Stepanakert. Azerbaijan responded by declaring a partial military mobilization a day later.
Yerevan has accused Ankara of having a “direct presence on the ground” and supplying its ally Baku with weapons, including drones -- a claim denied by Azerbaijan.
Turkish President Recep Tayyip Erdogan on September 28 called on Armenia to immediately end its "occupation" of the region and withdraw, saying this was the only way to secure peace.