Armenia and Azerbaijan reported heavy destruction and casualties on September 27 after clashes in the disputed region of Nagorno-Karabakh that touched off a flurry of diplomacy aimed at calming the tensions.
The two countries declared martial law and accused each other of initiating the clashes, which claimed at least 23 lives.
Military officials in Nagorno-Karabakh confirmed that 16 of its servicemen were among the dead and more than 100 were wounded. Armenian rights activists said earlier that an ethnic Armenian woman and child had also been killed.
Azerbaijan said five members of one family were killed in shelling by Armenian armed forces. According to the Prosecutor-General's Office, 19 civilians have been wounded and hospitalized.
The fighting was the worst escalation of violence since 2016 and drew swift responses from European countries, Russia, the United Nations, and the United States.
The U.S. State Department expressed alarm over reports of "a large-scale military action" that resulted in "significant casualties," including civilians.
"The United States condemns in the strongest terms this escalation of violence," State Department spokeswoman Morgan Ortagus said in a statement.
Ortagus said Deputy Secretary Stephen Biegun called the foreign ministers of Azerbaijan and Armenia "to urge both sides to cease hostilities immediately" and use existing communication links between them to avoid further escalation and "unhelpful rhetoric and actions that further raise tensions on the ground," Ortagus said.
UN Secretary-General Antonio Guterres said he was "extremely concerned over the fresh resumption of hostilities," adding his voice to condemnations of the violence from Germany, France, and Italy and calls for an immediate cease-fire.
Armenian Prime Minister Nikol Pashinian said earlier that 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.
Clashes broke out around 7 a.m. between Azerbaijani and Armenian forces over the breakaway region, which is inside Azerbaijan but run by ethnic Armenians.
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.
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 Defense Ministry spokesman Artsrun Hovhannisian said Azerbaijani forces launched missile attacks 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 Stepanakert," Hovhannisian said during a news conference.
Azerbaijani Foreign Minister Ceyhun Bayramov spoke by phone with Russian Foreign Minister Sergei Lavrov, who expressed concern about the situation in the region and "stressed the urgency of restoring ceasefire regime." Bayramov said Armenian armed forces had violated the cease-fire.
Russia, which regards Yerevan as a strategic partner, called on both sides to "immediately halt fire and begin talks to stabilize the situation."
Turkey, a close ally of Baku, said Armenia must immediately cease hostility toward 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.
"We believe this conflict can be resolved through peaceful negotiations, but Armenian side has shown no interest so far other than continuing to occupy parts of Azerbaijan," Ibrahim Kalin, President Recep Tayyip Erdogan's spokesman, told Reuters, calling for the Minsk Group countries to put pressure on Armenia.
The Minsk Group is a platform established by the Organization for Security and Cooperation in Europe (OSCE). Ortagus also called on the two sides to work with the Minsk Group.
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 include troops supplied by Armenia. The region's claim to independence has not been recognized by any country.
In July a days-long flareup 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.