MOSCOW (AP) — Armenia and Azerbaijan agreed to a Russia-brokered cease-fire in Nagorno-Karabakh starting Saturday, but immediately accused each other of derailing the deal intended to end the worst outbreak of hostilities in the separatist region in more than a quarter-century.

The two sides traded blame for breaking the truce that took effect at noon (0800 GMT) with new attacks, and Azerbaijan’s top diplomat said the truce never entered force.

The cease-fire announcement came overnight after 10 hours of talks in Moscow sponsored by Russian Foreign Minister Sergey Lavrov. The deal stipulated that the cease-fire should pave the way for talks on settling the conflict.

If the truce holds, it would mark a major diplomatic coup for Russia, which has a security pact with Armenia but also cultivated warm ties with Azerbaijan. But the agreement was immediately challenged by mutual claims of violations.

Minutes after the truce took force, the Armenian military accused Azerbaijan of shelling the area near the town of Kapan in southeastern Armenia, killing one civilian. Azerbaijan’s Defense Ministry rejected the Armenian accusations as a “provocation.”

The Azerbaijani military, in turn, accused Armenia of striking the Terter and Agdam regions of Azerbaijan with missiles and then attempting to launch offensives in the Agdere-Terter and the Fizuli-Jabrail areas. Azerbaijan’s Foreign Minister Jeyhun Bayramov charged that “conditions for implementing the humanitarian cease-fire are currently missing” amid the continuing Armenian shelling.

Armenia’s Defense Ministry denied any truce violations by the Armenian forces.

The latest outburst of fighting between Azerbaijani and Armenian forces began Sept. 27 and left hundreds of people dead in the biggest escalation of the decades-old conflict over Nagorno-Karabakh since a separatist war there ended in 1994. The region lies in Azerbaijan but has been under control of ethnic Armenian forces backed by Armenia.

Since the start of the latest fighting, Armenia said it was open to a cease-fire, while Azerbaijan insisted that it should be conditional on the Armenian forces’ withdrawal from Nagorno-Karabakh, arguing that the failure of international efforts to negotiate a political settlement left it no other choice but to resort to force.

The foreign ministers of Armenia and Azerbaijan signed the truce in Moscow after Russian President Vladimir Putin had brokered it in a series of calls with President Ilham Aliyev of Azerbaijan and Armenia’s Prime Minister Nikol Pashinian.

Russia has co-sponsored peace talks on Nagorno-Karabakh together with the United States and France as co-chairs of the so-called Minsk Group, which is working under the auspices of the Organization for Security and Cooperation in Europe. They haven’t produced any deal, leaving Azerbaijan increasingly exasperated.

Speaking in an address to the nation Friday hours before the cease-fire deal was reached, the Azerbaijani president insisted on his country’s right to reclaim its territory by force after nearly three decades of international talks that “haven’t yielded an inch of progress.”

Fighting with heavy artillery, warplanes and drones has engulfed Nagorno-Karabakh, with both sides accusing each other of targeting residential areas and civilian infrastructure.

According to the Nagorno-Karabakh military, 404 of its servicemen have been killed since Sept. 27. Azerbaijan hasn’t provided details on its military losses. Scores of civilians on both sides also have been killed.

The current escalation marked the first time that Azerbaijan’s ally Turkey took a high profile in the conflict, offering strong political support. Over the past few years, Turkey provided Azerbaijan with state-of-the-art weapons, including drones and rocket systems that helped the Azerbaijani military outgun the Nagorno-Karabakh separatist forces in the latest fighting.

Armenian officials say Turkey is involved in the conflict and is sending Syrian mercenaries to fight on Azerbaijan’s side. Turkey has denied deploying combatants to the region, but a Syrian war monitor and three Syria-based opposition activists have confirmed that Turkey has sent hundreds of Syrian opposition fighters to fight in Nagorno-Karabakh.

In an interview with CNN Arabic aired Thursday, Azerbaijan’s president admitted that Turkish F-16 fighter jets have stayed on in Azerbaijan weeks after a joint military exercise, but insisted that they have remained grounded. Armenian officials had earlier claimed that a Turkish F-16 shot down an Armenian warplane, a claim that both Turkey and Azerbaijan have denied.

Turkey’s involvement in the conflict raised painful memories in Armenia, where an estimated 1.5 million died in massacres, deportations and forced marches that began in 1915. The event is widely viewed by historians as genocide, but Turkey denies that.

Turkey’s highly visible role in the confrontation worried Russia, which has a military base in Armenia. Russia and Armenia are linked by a security treaty obliging Moscow to offer support to its ally if it comes under aggression.

But at the same time, Russia has sought to maintain strong economic and political ties with oil-rich Azerbaijan and ward off Turkey’s attempt to increase its influence in the South Caucasus without ruining its delicate relations with Ankara.

Putin and Turkish President Recep Tayyip Erdogan have negotiated a series of deals to coordinate their conflicting interests in Syria and Libya and expanded their economic ties. Last year, NATO member Turkey took the delivery of the Russian S-400 air defense missiles, a move that angered Washington.

A lasting cease-fire in Nagorno-Karabakh would allow the Kremlin to stem Turkey’s bid to expand its clout in Russia’s backyard without ruining its strategic relationship with Ankara.

The Turkish Foreign Ministry said the deal was “an important first step, but cannot replace a lasting solution.”

“Since the beginning, Turkey has always underlined that it would only support those solutions which were acceptable to Azerbaijan,” it said.

While Turkey has aspired to join the Minsk Group talks as a co-chair, the statement issued by Armenia and Azerbaijan contained their pledge to maintain the current format of the peace talks.

Speaking in televised remarks after the talks, Armenian Foreign Minister Zohrab Mnatsakanyan emphasized that “no other country, in particular Turkey, can play any role.”