Armenia and Azerbaijan accused each other of violating a temporary ceasefire within minutes of it coming into force on Saturday.
The two countries agreed to a truce on Friday evening after 11-hour talks chaired by Russian Foreign Minister Sergei Lavrov in Moscow.
The ceasefire, to allow for the exchange of prisoners and the recovery of dead bodies in the disputed region of Nagorno-Karabakh, came into force at midday local time (10:00 CET) on Saturday.
In a statement released an hour after the truce started, the Azerbaijani Defence Ministry said that a number of populated areas were "under artillery fire by the Armenian armed forces".
The Azerbaijani military accused Armenia of striking the Terter and Agdam regions of Azerbaijan with missiles and then attempting to launch offensives in the Agdere-Terter and the Fizuli-Jabrail areas.
Azerbaijan's Foreign Minister Jeyhun Bayramov charged that “conditions for implementing the humanitarian cease-fire are currently missing” amid the continuing Armenian shelling.
But Armenia’s Defence Ministry denied any truce violations by the Armenian forces, and pointed the finger at Azerbaijan. A spokeswoman tweeted that "Azerbaijani units launched an assault on an area called 'Karakhambeyli' at 12:05".
The Armenian military accused Azerbaijan of shelling the area near the town of Kapan in southeastern Armenia, killing one civilian. Azerbaijan’s Defence Ministry rejected the Armenian accusations as a "provocation".
Both sides had earlier accused each other of shelling civilian areas before the ceasefire came into force.
Lavrov told reporters on Friday evening that the two parties will "begin substantive negotiations with the aim of achieving a peaceful settlement as soon as possible."
The international community has repeatedly called on Armenia and Azerbaijan to agree to an immediate and unconditional ceasefire.
Armenia and Azerbaijan fought a bloody war over Nagorno-Karabakh in the early 1990s which ended in a truce in 1994. Sporadic episodes of violence have since taken place.
The mountainous region lies in Azerbaijan but is controlled by ethnic Armenians backed by Armenia.
Violence between the two former Soviet states erupted again on September 27 with both sides blaming each other for the latest flare-up — the worst in decades.
At least 400 people have since been killed in the fighting and half of the region's population — about 70,000 — have been displaced.
The International Committee of the Red Cross — which will assist the two sides during the temporary ceasefire — said earlier this week "hundreds of key infrastructure like hospitals and schools" have either been destroyed or damaged by heavy artillery.