Armenia and Azerbaijan have accused each other of violating a humanitarian ceasefire in the disputed region of Nagorno-Karabakh.
Both sides agreed had agreed a truce to start at midnight local time (20:00 GMT Saturday).
But an Armenian defence ministry spokeswoman said Azerbaijan broke the ceasefire after just four minutes by firing artillery shells and rockets.
Azerbaijan later said Armenia had broken the truce.
Both countries signed a Russian-brokered ceasefire last Saturday. However, clashes continued despite that accord.
Fighting flared last month over the territory, which is internationally recognised as part of Azerbaijan but run by ethnic Armenians. Hundreds have died.
This is the worst violence in the region since a six-year war over the territory ended with a ceasefire in 1994.
Earlier on Saturday, both nations continued to trade accusations over violations of the Russian-brokered truce agreed last weekend and doubts are likely to remain following the latest statements.
What is the latest agreement?
Both nations confirmed the humanitarian truce, although few other details were given.
Azerbaijan’s foreign ministry said the decision was based on statements by the presidents of the US, France and Russia, representing the OSCE Minsk Group – a body set up in 1992 and chaired by the three countries to mediate the Nagorno-Karabakh conflict.
Anna Naghdalyan, spokesperson for Armenia’s foreign ministry carried the same statement in a tweet, adding it welcomed efforts towards a “ceasefire and de-escalation of tension” in the conflict zone.
Russian Foreign Minister Sergei Lavrov, who negotiated last weekend’s accord, spoke to counterparts in both countries on Saturday and said they needed to “strictly follow” the earlier agreement.
French President Emmanuel Macron agreed, saying his country would pay “close attention” to the ceasefire.
What’s the latest on the ground?
“The enemy fired artillery shells in the northern direction from 00:04 to 02:45, (20:04 to 22:45 GMT Saturday) and fired rockets in the southern direction from 02:20 to 02:45,” Armenian defence ministry spokeswoman Shushan Stepanyan said on Twitter.
She later said that Azerbaijan launched an assault in the south of Nagorno-Karabakh on Sunday morning. “There are casualties and wounded on both sides.”
A statement from Armenia’s foreign ministry on Sunday said it was the second time Azerbaijan had broken a ceasefire, and said Armenia would take all “necessary measures” to bring about a ceasefire and ways of enforcing it “on the ground”.
Azerbaijan, however, accused Armenia of breaking the ceasefire by firing mortars and artillery during the night. “Azerbaijan has taken adequate response measures,” a defence ministry statement read.
The ministry later also said Armenian forces had launched attacks on Sunday morning, which Azerbaijan’s forces had repulsed.
Azerbaijan accused Armenia of a missile strike in the early hours of Saturday that killed at least 13 civilians and injured 45 in Ganja, a city far from the front lines.
A foreign ministry statement accused Armenia of “deliberate and indiscriminate targeting of civilians”.
Armenian officials denied the attack, and accused Azerbaijan of attacking civilian areas.
Ms Stepanyan posted a video on Facebook, which she said showed devastation in the Nagorno-Karabakh region, accusing the Azerbaijani Armed Forces of striking at civilians with missiles in areas including the Nagorno-Karabakh capital, Stepanakert.