Azerbaijan on Wednesday threatened to shoot down civilian planes flying to disputed Nagorny Karabakh if the separatist Armenian authorities who control the region reopen an airport there.
Azerbaijan considers Karabakh to be occupied by the Armenians, and Baku's state aviation agency said it has told the International Civil Aviation Organisation (ICAO) that the region's airspace was closed and any flights would be unauthorised.
"According to the law on aviation, it is even possible to physically destroy aeroplanes which are heading there," said Arif Mammadov, the director of Azerbaijan's Civil Aviation Administration, in comments to local media.
"We asked the ICAO to notify the opposing side in order to prevent incidents," he said.
The separatist Karabakh authorities have been rebuilding the airport near their capital Stepanakert and plan to restart commercial flights to Yerevan in May.
The airport has been closed since the outbreak of the Karabakh war in the early 1990s, which saw ethnic Armenian forces backed by Yerevan seize control over the region from Baku amid fighting that left an estimated 30,000 dead.
An official at the separatist Karabakh presidential office said that "criminal" threats would not stop the planned flights, which are set to begin amid increasing tensions and exchanges of gunfire across the ceasefire line which has divided the two sides since the end of the war.
"We are determined to open the airport, no matter whom it vexes in Azerbaijan," the official, David Babaian, told the PanArmenian news agency.
"Any slight attempt Azerbaijan might take will be fraught with unpredictable repercussions for Azerbaijan itself," he said.
Azerbaijan has threatened to use force to win back Karabakh if peace talks do not yield satisfactory results, while Armenia has warned of large-scale retaliation if Baku launches any military action.