In an address to the nation, Azerbaijani President Ilham Aliyev says Armenia has "violated" the US-brokered ceasefire.
But Armenia's defence ministry says Azerbaijani forces have violated the truce with artillery fire on combat positions in various parts of the frontline.
A third attempt at halting weeks of fighting over Nagorno-Karabakh has collapsed quickly with Armenia and Azerbaijan trading accusations of violating the ceasefire within minutes.
