Ethnic-Armenian forces in the breakaway region of Nagorno-Karabakh have accused Azerbaijan's military of breaking a ceasefire brokered by Russia.
Gunfire could be heard in social media footage from the territory's capital.
Azerbaijan dismissed the reports as "completely false".
The two sides are holding talks to negotiate the enclave's integration into Azerbaijan after Karabakh forces agreed to surrender following 24 hours of intense fighting.
A day after the truce came into effect, local Armenian forces said Azerbaijan was using "a variety of firearms, violating the agreement on the ceasefire".
They said shots could be heard in the centre of the region's major city, Khankendi, known as Stepanakert by Armenians.
Videos showed people in the city running for cover and what appeared to be small-arms gunfire could be heard in the background.
Independent observers have been unable to reach the territory since Azerbaijan started an effective blockade of the area in December 2022. Azerbaijan's defence ministry swiftly denied that fighting had resumed: "We strongly deny this disseminated information," it said.
Meanwhile, ethnic-Armenian and Azerbaijani delegations met in the town of Yevlakh, some 100km (60 miles) north of Khankendi, to discuss Nagorno-Karabakh's future.
Pictures on Azerbaijani state media showed the two delegations seated with representatives of Russia's peacekeeping mission.
Following the ceasefire, Azerbaijan intends to bring the breakaway region in the South Caucasus - where an estimated 120,000 ethnic Armenians live - under full control. Nagorno-Karabakh is internationally recognised as part of Azerbaijan.
Under the terms of the agreement, local Karabakh forces must commit to being completely disbanded as well as disarmed.
There is also a commitment to Armenian forces pulling out, even though its government denies having any military presence there.
Armenians fear that Azerbaijan taking control could lead to ethnic cleansing and Karabakh Armenians being forced to flee.
But Azerbaijan's President Ilham Aliyev said his country had nothing against the population, only their "criminal junta".
Russia said its peacekeepers had evacuated 5,000 people from dangerous areas since the offensive had begun, the country's Interfax news agency reported.
At least four peacekeepers were killed in shelling, including the mission's deputy commander, according to Russia's Kommersant newspaper.
President Aliyev expressed his condolences and told Vladimir Putin an investigation into their deaths would be carried out, the Kremlin said.