Fighters stand in a village of Stepanakert during the ongoing fighting between Armenian and Azerbaijani forces in Nagorno-Karabakh region. AFP
The escalation drew immediate international rebuke, with Russia accusing Baku of violating the brittle ceasefire and the European Union urging an "immediate cessation of hostilities".
Arch enemies Armenia and Azerbaijan fought two wars â€” in 2020 and in the 1990s â€” over Azerbaijan's Armenian-populated region of Nagorno-Karabakh.
In the aftermath of the latest war, Armenia was forced to cede swathes of territory it had controlled for decades, and Russia deployed some 2,000 peacekeepers to oversee a fragile truce, but tensions persist despite a ceasefire agreement.
Refugees of the Nagorno-Karabakh region look and sit in their beds in a centre for refugees in Yerevan. File/AFP
On Wednesday, new tensions flared as Azerbaijan said it had lost a soldier and the Karabakh army said two of its troops had been killed and more than a dozen injured.
The Azerbaijani defence ministry said Karabakh troops targeted its army positions in the district of Lachin, which is under the supervision of the Russian peacekeeping force, killing an Azerbaijani conscript.
The Azerbaijani army later said it conducted an operation dubbed "Revenge" in response and took control of several strategic heights in Karabakh.
The army of the breakaway statelet for its part accused Azerbaijan of violating a ceasefire and killing two soldiers and wounding another 14.