Azerbaijan — Armenian and Azerbaijani forces exchanged rocket fire as fighting intensified over Nagorno-Karabakh on Sunday, with the breakaway region's capital and Azerbaijan's second-largest city bombarded.

Armenia said that Nagorno-Karabakh's main city Stepanakert, which has been under artillery fire since Friday, was hit again on Sunday and AFP journalists said there were regular explosions and clouds of black smoke rising in parts of the city.

Azerbaijan's defence ministry said Ganja, a city of more than 330,000 in western Azerbaijan, was also "under fire", while Armenian-backed separatist forces claimed to have destroyed an airbase there.

The two sides accused each other of targeting civilian areas, as the conflict appeared to be widening a week after heavy fighting broke out in the decades-old dispute over the ethnic-Armenian region.

Armenia and Azerbaijan have resisted international calls for a ceasefire and clashes have intensified in recent days, with both sides claiming victories on the front and saying they are inflicting heavy losses.

Sirens were sounding and explosions were heard at regular intervals in Stepanakert, where residents were taking shelter including several families in the basement of a church.

Armenia’s foreign ministry said Stepanakert and the Karabakh town of Martakert were under rocket attack and accused Azerbaijani forces of "the deliberate targeting of the civilian population”.

It said the Azerbaijani air force was also involved. Drones could be heard flying over Stepanakert.

Azerbaijan said Ganja was under fire, including from areas outside of Karabakh.

"Armenian forces struck Ganja with rockets from Armenian territory,” said Hikmet Hajiyev, an adviser to Azerbaijani President Ilham Aliyev.

He said Armenian forces had also used heavy artillery and rockets against the towns of Terter and Goradiz in Azerbaijan.

‘Decisive moment’ 

Karabakh’s separatist forces said they had targeted and destroyed an airbase in Ganja, but Baku denied this as a "provocation” and said civilian infrastructure and housing had been hit.

Azerbaijan’s ally Turkey accused Armenia of "targeting civilians” in Ganja and reiterated support for its fellow Turkic and Muslim country as "one nation, two states”.

Karabakh leader Arayik Harutyunyan warned that it would now consider "military facilities in Azerbaijan’s big cities” as legitimate targets.

"I call on the residents of these cities to immediately leave,” Harutyunyan said in a post on Facebook.

Harutyunyan announced on Saturday that he was heading to the front to join the fighting.

Azerbaijani officials claimed on Sunday that he had been "seriously wounded” while in a bunker hit by bombing, but his office denied this.

Azerbaijan claims to have made gains in Karabakh in recent days, with its defence ministry saying that 14 settlements have been taken as well as a strategically important plateau.

In an address to the country on Saturday, Prime Minister Nikol Pashinyan said Armenians were facing a "decisive moment” and called for the nation to come together.

Armenia on Saturday announced the deaths of 51 more separatist fighters, taking the number of reported fatalities on both sides above 240, including more than 30 civilians.

Azerbaijan on Sunday said two more civilians had been killed in shelling on the southern town of Beylagan, where a journalist working with AFP saw residents picking through the rubble of destroyed homes.

"I was baking bread when I heard explosions, I opened the door and saw that bombs were falling right into the yard,” said one woman, showing journalists the blown-out windows and partially collapsed roof of her home.

Praying for peace 

In Armenia’s majority-Christian capital Yerevan, residents gathered in churches for services on Sunday to pray and light candles.

"The situation in the country is very critical,” Aytsemik Melikyan told AFP outside the Saint Sarkis Church. "I came to ask God for peace, for our country and our soldiers.”

Russia, the United States and France — who co-chair a mediation group that has failed to bring about a political resolution to the conflict — have called for an immediate halt to the fighting.

Armenia has said it is "ready to engage” with mediators but Azerbaijan — which considers Karabakh under Armenian occupation — says Armenian forces must fully withdraw before a ceasefire can be brokered.

Karabakh’s declaration of independence from Azerbaijan during 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 ceasefire agreement.

The breakaway province is not acknowledged as independent by any country — including Armenia — and Karabakh said on Saturday that international recognition was "the only way towards peace and security in the region”.

Armenia has accused Turkey of dispatching mercenaries from Syria and Libya to the fighting — an allegation confirmed and denounced by Russia and France.

The Britain-based Syrian Observatory for Human Rights, a monitoring group, says more than 70 Turkey-backed fighters have been killed in the clashes in Nagorno-Karabakh