Armenia and Azerbaijan have both reported incidents on Tuesday and early Wednesday morning (11-12 January) along their common border in the Kelbajar region.
Azerbaijan says that one of its soldiers was killed on Tuesday morning, and Armenia confirmed that three of its soldiers have died in the 24 hour period from 11 to 12 January.
The three Armenian soldiers were named as Vahan Vachagan Babayan (born in 2003), Arthur Artyom Mkhitaryan (born in 2002) and Junior Sergeant Rudik Rafik Gharibyan (born in 2002).
The killed Azerbaijani soldier was named as Ayaz Nazarov, born in 1998,
Both sides speak of heightened tension.
It is not yet clear what triggered the incidents, which appear to be more serious than previous skirmishes.