The Armenian Defense Ministry reported early on Tuesday morning that Azerbaijani artillery shells were falling on Armenian soil.
"Beginning at 12:05 am on September 13, units of the Azerbaijani Armed Forces began intensive shelling using artillery, large-caliber small arms in the direction of Armenian positions near Goris, Sotk and Jermuk," the ministry said in a statement, adding that the Azerbaijanis were also using drones.
The three cities are in the part of Armenia that separates the Azeri Nakhchivan exclave from the rest of Azerbaijan, and not far from the contested Nagorno-Karabakh territory, an Armenian-majority region inside of Azerbaijan where a breakaway Artsakh Republic has persisted for decades.
By contrast, the Azerbaijani Defense Ministry accused Armenia of "a large-scale provocation in the Dashkesan, Kalbajar and Lachin directions of the Azerbaijani-Armenian state border" on the night of September 12.
"As a result, there were losses among the personnel, military infrastructure was damaged," it said, adding that Azerbaijani Army forces "are taking the necessary measures to suppress the firing points of the Armenian armed forces and prevent the expansion of the scale of military clashes."
In video posted on social media that is purported to be of the shelling, numerous explosions can be seen and heard.
More violations of the ceasefire by Baku were reported last month by the Russian Defense Ministry, which noted them to be in the area of Sarybab Heights in Nagorno-Karabakh.
Azerbaijan and Armenia engaged in a fierce armed conflict between September and November 2020 over the territory, in which both sides sustained considerable losses, but which resulted in Baku seizing or being ceded all remaining territory around Nagorno-Karabakh that had been occupied by Armenian troops.
Moscow brokered the ceasefire on November 11, 2020, and Russian peacekeepers have patrolled the area ever since, ensuring access between Armenia and Nagorno-Karabakh via the 3-mile-wide Lachin corridor.
During the Soviet period and the Russian Empire before it, the entire territory had been part of a single country, so the ethnic exclaves that dot the region were not of major concern. However, when the USSR was dissolved in December 1991 and the 15 constituent socialist republics became independent, the issue became decisive, and wars flared between several newly independent states, including between Yerevan and Baku from 1992 until 1994, when a ceasefire ended fighting but failed to settle the issue decisively.