Armenia and Azerbaijan declared martial law on September 27 after both sides reported heavy destruction and casualties in clashes in the disputed region of Nagorno-Karabakh.
Armenian Prime Minister Nikol Pashinian said the government decided to declare martial law and a total mobilization after Azerbaijan launched an air and artillery attack on civilian settlements in Nagorno-Karabakh, including in the regional capital of Stepanakert.
Azerbaijan's parliament followed with its own introduction of martial law across the country along with curfews, said Hikmat Haciyev, an aide to the president.
The moves come after morning clashes between Azerbaijani and Armenian forces over the breakaway region, which is inside Azerbaijan but run by ethnic Armenians.
Both sides have reported casualties, prompting international calls for the two sides to stop fighting and return to negotiations.
Azerbaijan said it had launched a military operation in response to shelling along the so-called Line of Contact that separates Armenian and Azerbaijani forces on the front line of Europe's longest-running conflict.
Armenia's Defense Ministry said that its troops shot down two Azerbaijani helicopters and three drones, a claim rejected by Baku.
"Our response will be proportionate, and the military-political leadership of Azerbaijan bears full responsibility for the situation," the Armenian Defense Ministry said in a statement.
Azerbaijan's Defense Ministry said its forces were “taking retaliatory measures and our troops are in full control of the operational situation.”
The ministry said that “fierce battles are ongoing all along the front line.”
A spokesman for the Armenian Defense Ministry said an Armenian woman and child were killed in Nagorno-Karabakh.
The Armenian government, as part of its martial law declaration, is requiring local media to cite only official Armenian information about military-related reports and is barring the use of Azerbaijani or outside sources.
Armenian Foreign Ministry spokeswoman Anna Naghdalian and Armenian Defense Ministry spokesman Artsrun Hovhannisian said Azerbaijani forces launched missile attacks beginning around 7 a.m. along the Line of Contact and said civilians and civilian infrastructure in Stepanakert had been targeted.
"There has been significant damage to buildings in certain parts of Nagorno-Karabakh and [its capital] Stepanakert," Hovhannisian said during a joint news conference with Naghdalian.
Turkey, a close ally of Baku, said Armenia must immediately cease hostility towards Azerbaijan that will "throw the region into fire.”
Pashinian also called on the international community to ensure that Turkey does not involve itself in the conflict. Turkey had earlier sharply criticized Armenia, saying Yerevan was an obstacle to peace and vowing to continue its support for Baku.
Turkish President Recep Tayyip Erdogan's spokesman Ibrahim Kalin addressed the flare-up in comments to Reuters.
"We believe this conflict can be resolved through peaceful negotiations, but the Armenian side has shown no interest so far other than continuing to occupy parts of Azerbaijan," Kalin said. "That occupation must end, everybody knows where the solution lies, and the Minsk Group countries must put pressure on Armenia to stop violating international law."
He added: "Turkey remains fully in solidarity with Azerbaijan."
The Minsk Group is a platform established by the Organization for Security and Cooperation in Europe (OSCE). It is chaired by the United States, France, and Russia.
Russia called on both sides to "immediately halt fire and begin talks to stabilize the situation."
Russian Foreign Minister Sergei Lavrov “is conducting intensive contacts in order to induce the parties to cease fire and start negotiations to stabilize the situation,” Foreign Ministry spokeswoman Maria Zakharova said.
Russia, which has a military base in Armenia, regards Yerevan as a strategic partner in the region.
EU Council President Charles Michel said reports of the hostilities were a serious concern.
"Military action must stop, as a matter of urgency, to prevent a further escalation," Michel said on Twitter. "An immediate return to negotiations, without preconditions, is the only way forward."
France and Germany expressed concern over the confrontation, while Iran also called for an end to the fighting and said it was ready to facilitate talks and a cease-fire.
Pope Francis also reacted to the fighting, calling it "worrying news" and said he was praying for peace in the Caucasus and asking for "steps of goodwill and brotherhood."
Nagorno-Karabakh and seven adjacent districts of Azerbaijan were seized by Armenian-backed separatists who declared independence amid a 1988-1994 conflict that killed at least 30,000 people and displaced hundreds of thousands.
Since a fragile, Russian-brokered truce in 1994, the region has been under the control of ethnic Armenian forces that Azerbaijan says includes troops supplied by Armenia. The region's claim to independence has not been recognized by any country.
In July, a days-long flare-up that included drone attacks and heavy artillery fire killed at least 17 people, mostly soldiers on both sides but including at least one civilian, in the worst fighting in about four years. Since then, periodic skirmishes have taken place in the region.