https://www.bbc.com/news/world-europe-54874162Russia has a military base in Armenia, but also has strong ties to Azerbaijan.
The downing happened close to Nakhchivan, which is not near the current clashes in Nagorno-Karabakh.
Azerbaijan's foreign ministry said the helicopter had been flying at a low altitude during hours of darkness.
A "Manpads" shoulder-launched missile brought it down, the report said.
"Helicopters of the Russian air force had not been previously sighted in the area," the ministry said.
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