Armenia attacked Azerbaijan's cities and villages in violation of the cease-fire deal brokered by Russia that seeks to end the worst outbreak of hostilities in the separatist Nagorno-Karabakh region, the Washington Post reported.

The Azerbaijani Defense Ministry said that Armenian forces shelled villages in the Aghdam, Terter, Aghjabedi and Fizuli regions of Azerbaijan. Azerbaijani authorities earlier accused Armenian forces of firing missiles at Ganja, the country’s second-largest city, and the city of Mingachevir overnight.

Nine civilians were killed and more than 30 others wounded in Ganja, officials said. Azerbaijani President Ilham Aliyev called the attack on the city “a war crime” and a “gross” violation of the cease-fire on Twitter, promising “a befitting retaliation.”

Armenian military officials denied attacking Ganja and said the territory’s army is observing the cease-fire. They accused the Azerbaijani side for shelling Khankendi, the region’s capital, and other towns in violation of the truce.

The recent bout of fighting between Azerbaijani and Armenian forces started 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 the control of ethnic Armenian forces backed by Armenia.

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

The cease-fire took effect at noon Saturday, after talks in Moscow that were 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 had held, it would have marked a major diplomatic coup for Russia, which has a security pact with Armenia but also cultivated warm ties with Azerbaijan.

However, minutes after the cease-fire took force, both sides accused each other of continuing attacks in violation of the deal.

The situation in the region was “relatively calm” on Sunday morning, according to Nagorno-Karabakh leader Arayik Harutyunyan, with only minor hostilities along the front line. But it was unclear whether the calm would last, he said.

Later Sunday, Armenian Defense Ministry spokeswoman Shushan Stepanian reported attacks by Azerbaijani forces on southern and northeastern directions, saying that Armenian Armed forces “resolutely suppress all enemy operations.”

Armenian army in a statement Sunday promised a “disproportionately harsh” response if Azerbaijan “continues to violate the cease-fire.” The Azerbaijani Defense Ministry said that “the political and military leadership of Armenia bears the responsibility for the aggravation of the situation in the region.”

Azerbaijan’s president said in an interview with the Russian RBC news outlet that “if the Armenian side is committed to the cease-fire regime ... the phase of political settlement will begin.”

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