The capital of the breakaway Nagorno-Karabakh region was targeted in heavy strikes by Azerbaijani forces overnight and Wednesday morning, an AFP correspondent said.

Heavy fighting between Armenian and Azerbaijani forces broke out over the disputed region more than a week ago and both sides have accused the other of targeting civilian areas.

The shelling in Stepanakert was the most intensive nighttime bombardment in the city of more than 50,000 people since last weekend, a resident told AFP.

Nearly every hour throughout the night sirens rang out in Stepanakert, which was almost completely dark.

The sirens were followed by a succession of heavy explosions, but it was not immediately clear whether the city had been struck by rockets, missiles or other weapons. 

After a two-hour break Wednesday morning, one or more drones could be heard flying over the city at around 10:00 am (0600 GMT), buzzing with the recognizable sound of a lawn mower.

Two medium-intensity explosions were heard -- most likely strikes by the drones -- with one targeting a power station in the city's northeast, AFP journalists said.

A plume of grey smoke rose from the area around the station which was repeatedly struck in recent days.

Armenian forces have sought to shoot down the unpiloted aircraft with automatic weapons and air-defence systems.

At least three houses next to each other were destroyed by a powerful explosion but there were no casualties.

Locals suggested that a Smerch (Tornado) rocket -- a Soviet-designed 300-mm rocket system -- could have been behind the destruction.

Another rocket landed in the garden of a house, leaving a roughly 10-metre crater in the ground. The sole victim appeared to be a dog whose gutted remains were lying nearby.

Over the past few days, Karabakh's separatist authorities have repeatedly denounced the use of Smerch rockets. Some of the unexploded rockets were seen sticking out of the ground.