TEHRAN (Iran News) – Armenian and Azerbaijani forces were engaged in fierce clashes Saturday as fighting over the disputed Nagorno-Karabakh region intensified after its main city came under heavy shelling.

The leader of the breakaway province said he was heading to the front and that the “final battle” for the region had begun, seven days after new fighting erupted in the decades-old dispute, AFP reported.

Armenia’s Defense Ministry said Karabakh’s separatist forces had repelled a “massive attack” by Azerbaijan in one area of the frontline and had launched a counter-offensive.

“Heavy fighting is ongoing on other flanks,” Defense Ministry spokeswoman Shushan Stepanyan said.

Azerbaijan’s Defense Ministry said its forces had “captured new footholds” and that the Armenians had “suffered serious losses in manpower and military hardware”.

The clashes came after the regional capital Stepanakert came under artillery and rocket fire on Friday. Residents hid in shelters and on Saturday were clearing up wreckage and sweeping up the shattered glass windows of their homes and shops.

At least one person was reported killed in the shelling.

Both sides have been accused of hitting civilian areas, with Azerbaijan saying Saturday that Armenian artillery had shelled 19 of its settlements overnight.

The International Committee of the Red Cross said on Friday that civilians are bearing the brunt of the surge in violence.

“Since the escalation started, the ICRC has provided emergency medical supplies to hospitals and body bags to the forensic bureau in Nagorno-Karabakh. We are currently trying to assess health-related and other humanitarian needs, including the situation of those who have left their homes. Our ability to move in the field is limited because of the intensity of fighting and the volatility of the situation,” said Bertrand Lamon, ICRC’s head of mission in Nagorno-Karabakh.

The new fighting erupted last Sunday and mounting international calls for a halt to the hostilities and a return to negotiations over the dispute have gone unanswered.

The leader of the breakaway province, Arayik Harutyunyan, said he was headed to join the “intensive fighting” on the frontline.

The Armenian side has reported 158 military deaths and said 14 civilians have been killed. Azerbaijan has reported 19 civilian deaths but has not confirmed any fatalities among its troops.

Russia, the United States and France – whose leaders co-chair a mediation group that has failed to bring about a political resolution to the conflict – called on the warring sides this week to immediately agree a cease-fire.

Iranian Foreign Minister Mohammad Javad Zarif and his Russian counterpart Sergei Lavrov talked by phone on Friday and expressed concern over the involvement of Syrian and Libyan militants in the Nagorno-Karabakh conflict, Russia’s Foreign Ministry said.

Two Syrian sources have told Reuters that Turkey is sending Syrian militant to support Azerbaijan, something both Ankara and Baku have denied.

Armenia said Friday it was “ready to engage” with mediators but Azerbaijan – which considers Karabakh under Armenian occupation – has said Armenian forces must fully withdraw before a cease-fire can be brokered.

Karabakh’s declaration of independence from Azerbaijan amid the collapse of the Soviet Union sparked a war in the early 1990s that claimed 30,000 lives.

Talks to resolve the conflict have made little progress since a 1994 cease-fire agreement.