Nikol Pashinyan, the Armenian prime minister, declared a state of emergency and mobilized the country’s male population. “The enemy has started an attack,” he wrote on Facebook. He said, “This aggression was preplanned.”
Mr. Pashinyan said the military of the Karabakh region, which claims to be an independent state but is mostly unrecognized, had repelled an attack. In a televised address, Mr. Pashinyan said civilians had suffered but did not specify how many. In Karabakh, the authorities said fighting had killed 16 of their soldiers and wounded about 100 more.
Azerbaijan said it was responding to cross-border artillery shelling. Its Ministry of Defense then issued a statement saying it had begun a “counterattack” with tanks, helicopters and rocket artillery.
In a statement carried by Russian news agencies, Azerbaijan said the military operation had destroyed “troops, military objects and equipment of the Armenian armed forces” near the border as well as deeper inside the country. It said it destroyed 12 short-range antiaircraft installations in Armenia.
Azerbaijan’s state news agency, Azertac, carried a statement by President Ilham Aliyev airing grievances against Armenia, including an accusation that Armenia was settling members of its diaspora in the disputed Karabakh region.
“It is as a result of Armenia’s hypocritical, unconstructive and false policy that the negotiations have actually stopped” for a settlement to the long-running conflict, it said. “They are deliberately provoking us, and they will see the bitter consequences.”
In past flare-ups, both sides have exaggerated their successes and the scale of their enemies’ violations of cease-fire agreements, though the potential for a wider war has always been clear. The Karabakh region maintains a system to call up nearly its entire male population as minutemen, and this mobilization was announced Sunday morning. Azerbaijan said 14 of its civilians had been killed or wounded.