Azerbaijan on Thursday launched its heaviest missile strikes in a month of fighting on the largest city in its Armenian-populated breakaway region of Nagorno-Karabakh, separatist officials said.

“Azerbaijan struck Stepanakert for several hours, tens of missiles hit the city,” Karabakh’s rights ombudsman Artak Beglaryan told AFP.

“Civilians were injured as a result of the strike, the heaviest during the recent fighting,” he added.

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More than 130 civilians have been killed and thousands displaced in fresh clashes that erupted last month between Azerbaijani and Armenian forces over their decades-long conflict for control of the disputed territory.

Azerbaijan has noted that 26 civilians, including children and women, were killed earlier this week in Armenian missile strikes on the cities of Ganja and Barda.

Meanwhile, Armenia has denied carrying out the attacks.

The Azerbaijani Presidency on Thursday said that “under the initiative of (President) Ilham Aliyev, the Azerbaijani side handed bodies of 30 troops” killed in fighting to Armenia.

“Armenia has failed to show good will in that matter,” but thanks to Russian mediation has agreed to open a humanitarian corridor for the evacuation of Azerbaijani soldiers’ bodies from battlefields,” Aliyev’s foreign policy adviser Hikmet Hajiyev told journalists.

Armenian Defence Ministry Spokeswoman Shushan Stepanyan confirmed that the handover mediated by Russia and the Red Cross and added that the Armenian side was ready to return bodies of slain Azerbaijani soldiers.

Both sides have accused each other of failing to respect three separate ceasefire agreements mediated  by Russia, France and the United States this month.

Moscow, Paris, and Washington co-chair the Minsk Group of mediators that has failed to bring about a lasting breakthrough since a 1994 ceasefire.

Armenian and Azerbaijani foreign ministers, Zohrab Mnatsakanyan and Jeyhun Bayramov were due to meet on Thursday with the Minsk Group co-chairs in Geneva.

The Azerbaijani foreign ministry said Bayramov postponed the meeting until Friday and said that he would not meet directly with his Armenian counterpart.

Nagorno-Karabakh seceded from Baku in a war in the 1990s that left 30,000 people dead.

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Karabakh and Azerbaijan’s seven districts surrounding the mountainous province have since remained under the control of Armenian separatists, but is internationally recognized as part of Azerbaijan’s sovereign territory.

At least 1,252 people from both sides have been reported dead in the recent flare-up that began last month, the deadliest since the 1994 ceasefire.

The death toll is believed to be substantially higher with Russian President Vladimir Putin saying last week that close to 5,000 people had been killed.