Rivals accuse each other of breaking the truce, following the cease-fire agreement over the disputed Nagorno-Karabakh.
The agreement clinched after marathon talks advocated by the Russian government to halt the fighting and allow both parties to swap the dead and prisoners.
Armenian accused the Azeris of shelling a settlement in Armenia, and claim the Azeris broke the truce 5 minutes before it could take effect on Saturday.
AFP news agency reports, loud explosions rocked Stepanakart, the central of Nagorno-Karabakh around 11:30 pm local time.
Previously, Armenia and Azerbaijan agreed on a cease-fire, starting on Saturday both parties made a deal to exchange prisoners and bodies of those killed in the conflict.
Sergey Viktorovich Lavrov, Russian Foreign minister mediated the negotiations, following 10 hours of talk, both Azerbaijan and Armenia have reached a ceasefire deal on Saturday.
Under the international LAW, Nagorno-Karabakh belongs to Azerbaijan but due to Armenian influence and their majority population in the region, rejects the rule and runs the area based on the Armenian policy.