Emergencies personnel work in a damaged area of the city of Ganja after Armenian rocket strike. AFP

Armenia's president headed to Brussels for talks with the European Union and NATO military alliance on Wednesday in a renewed drive to end the heaviest fighting since the 1990s over the mountain enclave of Nagorno-Karabakh.

As part of a wide diplomatic push from major global powers, the Azeri and Armenian foreign ministers also flew to Moscow for talks with Russia, which has brokered two ceasefires but failed to end clashes killing hundreds of people in the last month.

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Armenian president to discuss Nagorno-Karabakh with EU, NATO

Nagorno-Karabakh ceasefire under severe strain after new fighting

12 civilians killed, 40 wounded in Ganja by Armenia shelling Azerbaijan

The warring sides' foreign ministers then go to Washington for talks on Friday involving US Secretary of State Mike Pompeo, which has raised hopes of a breakthrough.

Armenia, which has a defence pact with Russia, has accused Turkey of sending mercenaries to fight in the conflict.

Both sides reported new fighting on Wednesday in and around Nagorno-Karabakh, a breakaway territory within Azerbaijan that is populated and controlled by ethnic Armenians.

Azerbaijan denied one of its military planes was shot down.

The fighting has raised fears of a wider war in the South Caucasus drawing in Russia and Turkey, an ally of Azerbaijan, and increased concern about the security of pipelines in Azerbaijan that carry Azeri gas and oil to world markets.

Armenian President Armen Sarkissian was due to meet NATO Secretary General Jens Stoltenberg, EU foreign policy chief Josep Borrell and European Council President Charles Michel in Brussels, his office said.

"It is expected that the leadership of NATO and the European organisations will do everything possible to stop Azerbaijan's and NATO-member Turkey’s military actions, which will help bring to life the ceasefire agreements," it said.

Armenia, which has a defence pact with Russia, has accused Turkey of sending mercenaries to fight in the conflict.

Turkey has denied this, and says it has no direct role in the fighting. But its tough rhetoric has increased strains in relations with Russia and with Turkey's NATO allies, who have ignored Azeri calls for Ankara to have a peacemaking role.