More than two weeks of fighting between the Caucasus rivals has left almost 600 dead, including 73 civilians, according to a tally based on partial tolls from both sides.
Armenian and Azerbaijani forces have engaged in new fighting over the Nagorno-Karabakh region, as the Red Cross warned hundreds of thousands were already affected by the conflict.
The Russia-brokered truce is buckling despite mounting calls from world powers to halt the fighting. On Wednesday, the Kremlin tried to wrest control over the ceasefire as Russian Defence Minister Sergei Shoigu called on both his Armenian and Azerbaijani counterparts to comply with the ceasefire agreement in a phone call.
"Civilians are dying or suffering life-changing injuries," said International Committee of the Red Cross Eurasia regional director Martin Schuepp in a statement.
Occupied Karabakh is internationally recognised as part of Azerbaijan has been controlled by Armenians since a 1990s war that erupted as the Soviet Union fell.
But Azerbaijan has never hidden its desire to take back control of its territory and no state has ever recognised Nagorno-Karabakh's declaration of independence.
A Reuters television crew in Tartar in Azerbaijan said the city centre was being shelled.
An AFP correspondent there close to the front line reported hearing heavy shelling nearby and seeing a rocket launcher drive by as Azerbaijani forces sought to fire up into the mountains.
Azerbaijan accused Armenia of "grossly violating the humanitarian truce", which was agreed on Saturday to allow the sides to swap prisoners and bodies of those killed.
Defence Ministry spokesman Vagif Dargiahly said Armenia was shelling the Azerbaijani territories of Goranboy and Aghdam, as well as Tartar. Azerbaijani forces were not violating the truce, he added.
"We've been here for 16 days," said Akiif Aslamiv, 62, who has been hunkering down in a basement in Tartar. "Every day they shell us, even during the ceasefire. Today and yesterday it was non-stop."
Armenian Defence Ministry spokeswoman Shushan Stepanyan denied the accusation. She said Azerbaijan had resumed military operations "supported by active artillery fire in the southern, northern, northeastern and eastern directions".
The daily fighting has made a mockery of the ceasefire agreed between the Armenian and Azerbaijani foreign ministers in the early hours of Saturday in Moscow after 11 hours of talks.
Ankara has said it would favour four-way talks between Russia, Azerbaijan, Armenia and Turkey to try to solve a conflict in occupied Karabakh.
US Secretary of State Mike Pompeo is also among those urging a greater commitment to the ceasefire terms.
Pompeo urged the sides to observe a ceasefire agreed only four days ago in Moscow, while the group of powers seeking a solution to the conflict warned of "catastrophic consequences" unless immediate steps were taken.
The fighting has been the most intense since a 1994 ceasefire ended the initial post-Soviet war. Even a humanitarian truce to allow exchanges of prisoners and dead has been too much to implement.
"Homes, businesses and once-busy streets are being reduced to rubble," Red Cross Eurasia's Schuepp said.
He said hundreds of thousands of people across the region were affected, with healthcare services coming under strain and even attacked in some cases.
The United States calls on Azerbaijan and Armenia to implement their commitments to a ceasefire as agreed and cease targeting civilian areas, such as Ganja and Stepanakert. We deplore the loss of human life and remain committed to a peaceful settlement.— Secretary Pompeo (@SecPompeo) October 13, 2020
The Minsk Group, chaired by France, Russia and the US, said it was alarmed by the continued fighting and urged Azerbaijani President Ilham Aliyev and Armenian Prime Minister Nikol Pashinyan "to take immediate steps" fully implement the Moscow ceasefire.
Otherwise, there could be "catastrophic consequences for the region", it added in a statement.
Gela Vasadze, an analyst with Tbilisi-based think tank the Georgian Strategic Analysis Centre, said the current conflict was doing nothing to end the stalemate.
"What is clear is that Azerbaijan did achieve some military success, but not anything dramatic. We can't say Baku is close to taking control of Karabakh," he told AFP.
Turkey has strongly backed Azerbaijan and has said it wanted four-way talks between Russia, Azerbaijan, Armenia and Turkey.
"Since Russia is on Armenia's side and we, Turkey, support Azerbaijan, let's meet as a foursome to discuss resolving these problems," said Ibrahim Kalin, the Turkish presidency's spokesperson.
"If the Minsk Group hasn't been able to find a solution for more than 30 years, it's time to find a new mechanism."
Attempts at a ceasefire in the Nagorno-Karabakh region must be combined with a clear roadmap to end Armenian occupation. pic.twitter.com/DlnqUoBGpU— Ibrahim Kalin (@ikalin1) October 9, 2020
Armenia is part of a regional Russia-led security group but Moscow has so far refused to become drawn in to the conflict.
Yet analysts say Turkey's involvement will put further strain on the alliance between President Vladimir Putin and Turkish President Recep Tayyip Erdogan.
Iran, which has borders with both Armenia and Azerbaijan and has expressed alarm over the fighting, said a drone crashed near its border with Azerbaijan and investigators were trying to find out its origin.