The two countries had agreed on a humanitarian ceasefire from 18 October at 00.00 local time.
However, the Armenian Ministry of Defense today reported the firing of missiles and artillery by Azerbaijan.
The Azerbaijani Ministry of Defense later accused Armenia of non-compliance with the ceasefire.
The two sides agreed on a ceasefire last weekend, but it was soon violated.
More than 600 Armenian soldiers have died in the Nagorno-Karabakh conflict since the resumption of intense fighting on September 27, but the Azerbaijani side has not reported its casualties. Azerbaijani forces are reportedly being assisted by Turkish armed forces officers and Turkish-organized Syrian militants.
There have been hostile relations between Azerbaijan and Armenia since the 1990s, when there was a war over Nagorno-Karabakh, a predominantly Armenian population.
Nagorno-Karabakh, which was part of the Azerbaijani SSR during the Soviet era, has been a “de facto” independent Armenian republic since the early 1990s. Although Azerbaijan has not controlled Nagorno-Karabakh since the collapse of the USSR, it considers the Armenian region to be its territory. Nagorno-Karabakh is also considered by the international community to be part of Azerbaijan, and no country has recognized the region as an independent state.
Nagorno-Karabakh declared independence in 1991. Its secession from Azerbaijan contributed to the outbreak of war between Azerbaijan and Armenia. About 35,000 people lost their lives in the war, and more than a million people in both countries were forced to flee their homes.