Armenia's Foreign Ministry, however, denied its weapons or troops were in Nagorno-Karabakh and called reported sabotage and land mines in the region “a lie". Armenian Prime Minister Nikol Pashiyan charged that the main goal of Azerbaijan is to draw Armenia into hostilities.
Ethnic Armenian officials in Nagorno-Karabakh said in a statement that the region's capital of Stepanakert and other villages were “under intense shelling”. Video from the city showed a damaged residential building with shattered windows and damaged cars nearby.
Nagorno-Karabakh health officials said five people were killed and 80 others, including 15 civilians, were hospitalised with injuries. According to the region's human rights ombudsman Geghan Stepanyan, one child was among those killed and at least eight of those injured were children.
The Azerbaijani Prosecutor General's Office said Armenian forces fired at Shusha, a city in Nagorno-Karabakh under Azerbaijan's control, from large-caliber weapons, killing one civilian.
Neither claim could be independently verified.
Although Azerbaijan said the operation was limited to military targets, the Defence Ministry said “humanitarian corridors” had been created to evacuate the population.
Thomas de Waal, a senior fellow at the Carnegie Europe think tank, said the military operation could be part of a plan by Azerbaijan President Ilham Aliyev to get ethnic Armenians to leave the area.
Although he said it was still early to assess, it could be "a kind of limited military action which will try to coerce thousands of Armenians to flee to Armenia. And then Aliyev can achieve his objective of taking over Karabakh with not so much bloodshed," de Waal told The Associated Press.
Earlier Tuesday, Azerbaijan said six people were killed in two separate explosions in the region that is partly under the control of ethnic Armenian forces.
A statement from Azerbaijan's Interior Ministry, state security service and prosecutor-general said two highway department workers died before dawn when their vehicle was blown up by a mine and that a truckload of soldiers responding to the incident hit another mine, killing four.
Nagorno-Karabakh and sizable surrounding territories were under ethnic Armenian control since the 1994 end of a separatist war, but Azerbaijan regained the territories and parts of Nagorno-Karabakh during the 2020 fighting. That ended with an armistice placing Russian peacekeepers in Nagorno-Karabakh.
However, Azerbaijan alleges that Armenia has smuggled in weapons since then. The claims led to a blockade of the road connecting Nagorno-Karabakh to Armenia, causing food and medicine shortages in the region.
Red Cross shipments of flour and medical supplies reached Nagorno-Karabakh on Monday, but local officials said roads to the region were not fully open.
The hostilities come amid high tensions between Armenia and its longtime ally Russia. Armenia has complained repeatedly that the 2,000-member Russian peacekeeping force was unable or unwilling to keep the road to Armenia open, even though that duty was stipulated in the agreement that ended the 2020 war.
Armenia also angered Russia, which has a military base in the country, by holding military exercises with the United States this month and by moving toward ratifying the Rome Convention that created the International Criminal Court, which has indicted Russian President Vladimir Putin.
Russian Foreign Ministry spokeswoman Maria Zakharova denied Tuesday that Russia was told in advance of Azerbaijan's intention to mount the operation, saying the peacekeepers were notified only “a few minutes” before it began.
Kremlin spokesman Dmitry Peskov said Moscow was “concerned by a drastic escalation of tensions and the beginning of hostilities” in the region, and that the Russian military was in touch with their Armenian and Azerbaijani counterparts, trying “to bring back the process of settling (the conflict) back onto political-diplomatic track”.
De Waal said the Russian peacekeeping force “has lost probably its best officers to the war in Ukraine” but that "this breakdown in Armenia-Russian relations is a factor here".
“I think it encourages Azerbaijan to be bolder and it makes the Russians more ambiguous and less willing to to intervene. And, you know, it's quite possible indeed, that the Russians want to use a crisis to instigate regime change in Armenia,” he said.
Protesters gathered Tuesday in central Yerevan, the capital of Armenia, blocking streets and demanding that authorities defend Armenians in Nagorno-Karabakh.