A cease-fire took effect on Wednesday evening following two days of heavy fighting that marked the largest outbreak of hostilities in nearly two years.
Both sides accuse each other of provoking the clashes, which erupted on Tuesday and ended with international mediation overnight on Thursday.
Russia moved quickly on Tuesday to negotiate an end to the fighting, but a cease-fire it sought to broker has failed to hold with the parties trading blame for violations.
Azerbaijan's foreign ministry said in a statement that Armenian forces had fired on army positions in three districts of the country and that Armenian saboteurs planted mines in the areas.
The disaster comes as the country of three million people is still recovering from a 2020 war with Azerbaijan, which ended in a heavy defeat and sparked a political crisis.
Armenia-Azerbaijan conflict: Russia accuses Baku of violating ceasefire as new tensions explode over Karabakh
Arch enemies Armenia and Azerbaijan have fought two wars -- in 2020 and in the 1990s -- over Azerbaijan's Armenian-populated region of Nagorno-Karabakh.
Armenian acting Vice Premier Armen Gevorkyan's apparent move to secure support from the Kremlin came as protesters in the capital Yerevan took to the streets for a fresh day of rallies.
The country's veteran leader Serzh Sarkisian stood down on Monday from his new post as prime minister after days of protests by demonstrators who accused him of a blatant power grab.
According to Armenian law, lawmakers in the parliament, where Sarkisian's Republican Party have a majority, have a week to propose new candidates for PM and could hold a vote on May 2.
Residents of the capital, Yerevan, poured out on the streets to celebrate his stunning departure. People hugged and kissed each other, and motorists honked their horns.
Sarkisian, who served as president for a decade, was last week elected as prime minister with sweeping powers, triggering the protests.
Thousands of people in Armenia have been protesting for 10 days against ex-president Serzh Sarkisian taking up a new position as premier with sweeping powers.
With protests against Armenian PM Serzh Sarkisian escalating, here is all you need to know about the country's troubled history
Armenia is facing a deepening political crisis, after talks between Prime Minister Serzh Sarkisian and protest leader Nikol Pashinyan failed.
Armenian police said protest leader Nikol Pashinyan was forcibly taken from a protest rally, dismissing reports of his arrest as riot police and demonstrators clashed in Yerevan.
Armenia's political turmoil deepened as Prime Minister Serzh Sarkisian stormed out of talks with opposition leader Nikol Pashinyan, who was later forcibly removed from a protest.
Tens of thousands protested in Armenia's capital on Friday against what they say is a power-grab by ex-president Serzh Sarkisian, as police arrested 230 people.
Armenia's parliament today elected former president Serzh Sarkisian prime minister in a move that will see the 63-year-old maintain his grip on power despite major protests.
Armenians say up to 1.5 million of their kin were killed between 1915 and 1917, and have long sought international recognition that this was genocide.
Armenians have long sought recognition that some 1.5 million of their people were killed in a genocidal campaign in World War I by Ottoman forces to wipe them out in Anatolia.
Earlier on Friday, Sargsyan attended the World Food India event that Modi inaugurated.