This image taken from YouTube footage released by the Armenian Defense Ministry on Sept. 13, 2022, reportedly shows Azerbaijanian servicemen crossing the Armenian-Azerbaijani border and approaching the Armenian positions. ARMENIAN DEFENSE MINISTRY VIA AP

Fighting on the border between Armenia and Azerbaijan has killed about 100 troops as attacks on both sides Tuesday fed fears of broader hostilities breaking out between the longtime adversaries.

Armenia said at least 49 of its soldiers were killed; Azerbaijan said it lost 50.

The hostilities erupted minutes after midnight, with Azerbaijani forces unleashing an artillery barrage and drone attacks in many sections of Armenian territory, according to the Armenian Defense Ministry.

The ministry said fighting continued during the day despite Russia's attempt to broker a quick cease-fire. It noted that the shelling grew less intense but said Azerbaijani troops still were trying to advance into Armenian territory.

The ministry added that the Azerbaijani shelling damaged civilian infrastructure and also wounded an unspecified number of people.

Azerbaijan charged that its forces returned fire in response to "large-scale provocations" by the Armenian military, claiming that the Armenian troops planted mines and repeatedly fired on Azerbaijani military positions, resulting in unspecified casualties and damage to military infrastructure.

U.S. Secretary of State Antony Blinken expressed "deep concern" over the military action at the border in an overnight call with Azerbaijani President Ilham Aliyev, according to a State Department readout.

"Secretary Blinken urged President Aliyev to cease hostilities and stressed that the United States would push for an immediate halt to fighting and a peace settlement between Armenia and Azerbaijan," the readout said.

Azerbaijan and Armenia have been locked in a decades-old conflict over Nagorno-Karabakh, which is part of Azerbaijan but has been under the control of ethnic Armenian forces backed by Armenia since a separatist war there ended in 1994.

Azerbaijan reclaimed broad swaths of Nagorno-Karabakh in a six-week war in 2020 that killed more than 6,600 people and ended with a Russia-brokered peace deal. Moscow, which deployed about 2,000 troops to the region to serve as peacekeepers under the deal, has sought to maintain friendly ties with both ex-Soviet nations.

Azerbaijan's Aliyev held a meeting with military officials to discuss the situation. "It was noted that the responsibility for the current tension rests squarely with the political leadership of Armenia," his office said.

Turkey, an ally of Azerbaijan, also placed the blame for the violence on Armenia. Turkish Foreign Minister Mevlut Cavusoglu called for Yerevan to halt its "provocations," and Defense Minister Hulusi Akar condemned "Armenia's aggressive attitude and provocative actions."

Speaking in parliament early Tuesday, Armenian Prime Minister Nikol Pashinyan rejected the Azerbaijani claim that it was responding to Armenian provocations. He said his recent European Union-brokered talks with Aliyev in Brussels had revealed what he described as Azerbaijan's uncompromising stand.

Pashinyan noted that the Azerbaijani action followed his recent European Union-brokered talks with Aliyev in Brussels that revealed what he described as Azerbaijan's uncompromising stand.

As the fighting raged overnight, Pashinyan quickly called Russian President Vladimir Putin and later also had phone calls with French President Emmanuel Macron, European Council President Charles Michel, Iranian President Ebrahim Raisi and Blinken to discuss the hostilities.

The governor of Gegharkunik province, one of the regions that came under Azerbaijani shelling, said there was a 40-minute lull in the fighting, apparently reflecting Moscow's attempt to negotiate a truce, before hostilities later resumed.

The governor, Karen Sarkisyan, said that four Armenian troops in his region were killed and another 43 were wounded by the shelling.

The Armenian government said it would officially ask Russia for assistance under a friendship treaty between the countries and also appeal to the United Nations and the Collective Security Treaty Organization, a Moscow-dominated security alliance of ex-Soviet nations that includes Armenia.

Kremlin spokesman Dmitry Peskov refrained from comment on Armenia's request but added during a conference call with reporters that Putin was "taking every effort to help de-escalate tensions."

The Armenian Foreign Ministry said top officials from the security grouping held a meeting to discuss the fighting. Armenia's representative at the grouping emphasized during the meeting that Yerevan expects its allies to take "efficient collective steps to ensure security, territorial integrity and sovereignty of Armenia."

The Russian Foreign Ministry urged both parties "to refrain from further escalation and show restraint."

Moscow has engaged in a delicate balancing act, maintaining strong economic and security ties with Armenia, which hosts a Russian military base, while also developing close cooperation with oil-rich Azerbaijan.