Authorities in Azerbaijan’s breakaway Nagorno-Karabakh region have dismissed a statement by Baku warning that it declared the airspace over the territory closed.

David Babayan, deputy chief of staff to the president in the region’s self-declared government, said that planes were flying over Nagorno-Karabkh on November 13.

Azerbaijan announced on November 12 that it had closed the airspace after the Azerbaijani military shot down a helicopter belonging to the ethnic-Armenian-controlled territory’s forces.

Azerbaijan said the helicopter was shot down as it “attempted to open fire” on Azerbaijani forces and that its three crew members were killed.

The Nagorno-Karabakh “self-defense” forces said the helicopter was on a training mission, and Armenia’s Defense Ministry called the incident an “unprecedented provocation” by Azerbaijan.

Despite the Azerbaijani declaration of a no-fly zone, Armenian President Serzh Sarkisian made a surprise, but well-publicized visit to the Nagorno-Karabakh region on November 13.

Sarkisian’s press office said he traveled to the disputed region to visit units of the separatist defense forces and meet with the region’s leader.

Armenian-backed separatists seized the mainly Armenian-populated Nagorno-Karabakh region and surrounding areas from Azerbaijan during a war in the early 1990s that killed some 30,000 people and ended with a shaky cease-fire in 1994.

The fresh incident marks the first time a military aircraft has been shot down in the Nagorno-Karabakh region in at least 20 years.

The United States has expressed concern about the downing. U.S. State Department spokeswoman Jen Psaki said the incident was “yet another reminder” of the need to reduce tensions and respect a cease-fire in the region.

Psaki told reporters in Washington on November 12 that there could be “no military solution to the conflict.”

The Minsk Group of mediators from the Organization for Security and Cooperation in Europe (OSCE) — which is co-chaired by France, Russia, and the United States — said the incident showed the “urgency to intensify efforts to find a lasting settlement” to the decades-old conflict.

The European Union’s External Action Service issued a statement saying that “it is essential that all sides show restraint and avoid any actions or statements which could escalate the situation. Furthermore, we call for an investigation into this incident.”

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.

It would also contribute to fears of increasing volatility on Russia’s doorstep, with ongoing conflict in Ukraine that Western governments accuse Moscow of having a hand in and Russia’s unrecognized annexation of Crimea; continued tensions over Moldova’s breakaway Transdniester region, where Russian troops are still stationed; and Georgia still grappling with Russian-backed separatists who declared independence in the South Ossetia and Abkhazia regions.

With reporting by RFE/RL’s Armenian and Azerbaijan services, AFP, Interfax, and Trend.az