Azerbaijan and Armenia accused each other of shelling military positions and villages on Thursday, breaking a day of ceasefire in border clashes between the long-feuding former Soviet republics.
The Azeri defence ministry said one of its soldiers died, while Armenia's defence ministry said a civilian was wounded in Chinari village from an Azeri drone strike.
Prior to that, 15 soldiers from both sides and one civilian had died since Sunday in the flareup between nations who fought a 1990s war over the mountainous Nagorno-Karabakh region.
International concern is heightened because of the threat to stability in a region serving as a corridor for pipelines taking oil and gas from the Caspian Sea to global markets.
In a blizzard of rhetoric on both sides, Azerbaijan warned Armenia it might strike the Metzamor nuclear power station if its Mingechavir reservoir or other strategic outlets were hit.
The neighbours have long been in conflict over Azerbaijan's breakaway, mainly ethnic Armenian region of Nagorno-Karabakh. But the latest flareups are around the Tavush region in northeast Armenia, some 300 km (190 miles) from the enclave.
"With no gain in the battlefield, the Azerbaijani military units began shelling the villages ... deliberately targeting the civilian infrastructures and the population," Armenia's foreign ministry said in a statement on Thursday.
Its defence ministry accused the Azeri army of moving positions while using villagers as "human shields".
Azerbaijan denied targeting civilians and made the same accusation against Armenia of shelling villages. Reuters correspondent saw several partly-destroyed houses in the villages of Dondar Gushchu, Agdam and Alibeyli in Azerbaijan,
Ethnic Armenians in Nagorno-Karabakh declared independence during a conflict that broke out as the Soviet Union collapsed in 1991. Though a ceasefire was agreed in 1994, Azerbaijan and Armenia frequently accuse each other of attacks around Nagorno-Karabakh and along the separate Azeri-Armenian frontier.
Dozens of rounds of negotiations have not resolved the conflict and Azeri President Ilham Aliyev on Thursday sacked his veteran foreign minister, accusing him of "meaningless negotiations" with Armenia.