Armenian and Azerbaijani forces intensified their shelling  Thursday despite fresh calls from world leaders for an end to days of fighting over the disputed Nagorny Karabakh region that has left nearly 130 dead.

Police also deployed in large numbers in the streets of Stepanakert, the capital of the breakaway province, after two explosions, as drones buzzed overhead and sirens sounded during the night. The rival Caucasus nations have been locked in a bitter stalemate over the Karabakh region since the collapse of the Soviet Union when the ethnic Armenian region broke away from Azerbaijan.

The fiercest clashes between Armenian and Azerbaijani forces in years over the region ignited Sunday and confirmed deaths neared 130 as fighting raged for a fifth day. Armenian defence ministry spokesman Artsrun Hovhannisyan said fighting had "intensified" in the morning following fewer exchanges at night and that its troops had repelled Azerbaijani attacks.

He claimed that Armenian forces inflicted "enormous losses" over the night and into the morning, killing 350-360 Azerbaijani troops, downing three helicopters and destroying 15 armoured vehicles as well as drones. Azerbaijan's defence ministry, in turn, said its forces had carried out "crushing artillery strikes against Armenian forces' positions in the occupied territories" during the night.

It denied claims by Yerevan that one of its helicopters had been downed, crashing in Iran and said that fighters on the Armenian side had been "forced to retreat from previously held positions along the entire stretch of the frontline."

Threat of regional war

The two sides have accused the other of shelling civilian areas and ignored repeated calls from international leaders to halt fighting that carries the threat of drawing in regional powers Turkey and Russia.

Russian President Vladimir Putin and his French counterpart Emmanuel Macron, in a telephone conversation late Wednesday, issued the most recent call for a complete halt to fighting in Karabakh and said they were ready to intensify diplomatic efforts to help resolve the conflict. "Vladimir Putin and Emmanuel Macron called on the warring sides to halt fire completely and as soon as possible, de-escalate tensions and show maximum restraint," the Kremlin said.

Yerevan is in a military alliance of ex-Soviet countries led by Moscow and has accused Turkey of dispatching mercenaries from northern Syria to bolster Azerbaijan's forces in the Karabakh conflict. It also claimed earlier this week that a Turkish F-16 flying in support of Baku's forces had downed an Armenian SU-25 warplane, but Ankara and Baku denied the claim.

Armenian Prime Minister Nikol Pashinyan reiterated claims that mercenaries had joined the conflict, saying Azerbaijan and Turkey were fighting "with the help and involvement of foreign terrorist fighters."  "This terrorism equally threatens the United States, Iran, Russia, and France," he added.

Moscow has repeatedly called for an end to the clashes and on Wednesday offered to host negotiations. Russia also said it was concerned that members of illegal fighting groups, including from Syria and Libya, were being deployed to the fight.

Civilian casualties

Confirmed deaths have risen to 129 including civilians. Armenia has recorded the deaths of 104 soldiers and eight civilians. Azerbaijan hasn't repored any military casualties but said 17 civilians were killed as a result of Armenian shelling.

Though Azerbaijan did not admit to any deaths, an AFP journalist in the country's southern region witnessed the funeral of a soldier killed in the clashes. Pashinyan and Azerbaijani leader Ilham Aliyev have both rejected the idea of holding talks.

Karabakh's declaration of independence from Azerbaijan sparked a war in the early 1990s that claimed 30,000 lives, but it is still not recognised as independent by any country, including Armenia. Armenia and Karabakh declared martial law and military mobilisation Sunday, while Azerbaijan imposed military rule and a curfew in large cities.

Talks to resolve the conflict have largely stalled since a 1994 ceasefire agreement. France, Russia and the United States have mediated peace efforts as the "Minsk Group", but the last big push for a peace deal collapsed in 2010.