Images from the Nagorno-Karabakh military reportedly show the aftermath of heavy fighting in the Armenian separatist enclave in Azerbaijan.
The fighting erupted on Saturday killing dozens of people and threatening to shatter a fragile truce.
The Azeri Ministry of Defence claimed that six Armenian tanks were destroyed and more than 100 Armenian servicemen were killed and injured.
It added that 12 Azeri soldiers had been killed.
Armenia denied the figure of 100 casualties.
It is still unclear how many of the casualties are civilians.
Nagorno-Karabkh’s military claimed Armenian forces had shot down an Azeri helicopter. Baku later admitted that one of its Mi-24 helicopters had been struck down.
The Armenian Defence Ministry said: “The enemy, using tanks, artillery and aviation made attempts to get deep into the defence lines of the Nagorno-Karabakh Army of Defence and capture tactical positions. The enemy was thwarted.”
Armenia said 18 ethnic Armenians were killed and 35 injured.
MFA (@mfankr) April 2, 2016
The Azeri defence ministry claimed it had taken strategically important settlements, a claim denied by Armenia.
Both sides reported civilian casualties, accusing one another of violating the 1994 ceasefire.
MOD (@Karabakh_MoD) April 2, 2016
Russia, a key mediator in the conflict, has stepped in, with President Vladimir Putin calling for both sides to observe the ceasefire to ‘avert new casualties’.
Germany has also called for restraint.
There have been frequent threats by Azerbaijan to take Nagorno-Karabakh back by force.
It is unclear whether the clashes on Saturday marked a new phase in the conflict or merely a flare-up of tensions.
The ethnic war which began in the late 1980s claimed the lives of 30,000 people before ending in 1994 with a ceasefire but no final settlement.
Azerbaijan says 12 soldiers killed in fighting with Armenian forces over the separatist Nagorno-Karabakh region: https://t.co/MhWcYSKTYS— The Associated Press (@AP) April 2, 2016
VIDEO: Fighting last night between Armenian and Azerbaijani forces in Nagorno-Karabakh –
radiosvoboda</a> <a href="https://t.co/UV7jz1ruAZ">https://t.co/UV7jz1ruAZ</a></p>— Conflict News (Conflicts) April 2, 2016