Nagorno-Karabakh's largest city came under heavy shelling on Thursday, three sources working there said, as non-profit organization Reporters Without Borders, also known as Reporters sans frontières (RSF), called for the safe evacuation of civilians who it says are trapped in Stepanakert.

Writing on Twitter, Reporters Without Borders, a nonprofit group, called on the United Nations, the Council of Europe and Azerbaijan "to do everything possible" to allow an evacuation of civilians, including 80 local and foreign journalists.

At least 1,000 people and possibly many more have been killed since fighting broke out on September 27 in the region.

Two journalists reported that Stepanakert was under shelling all day. Some reporters were said to have left the city via a northern route because the main road to the Armenian capital, Yerevan, via the strategic region of Lachin was also under fire.

Heavy artillery was also said to have been used on the town of Martuni, known by Azerbaijan as Khojavend, while Shushi, or Shusha, the second largest city in the region, had reportedly been damaged by shelling.

Azerbaijan's defense ministry denied the accusations. It said instead that the city of Terter and a nearby village, as well as villages in the Aghdam region in the east of the conflict zone, had been shelled – a claim denied by ethnic Armenian forces.

Three ceasefires have failed to hold while attacks by the two warring sides resumed within hours of an agreement on October 30 to avoid deliberately targeting civilians.

Now in its sixth week, the conflict between Armenia and Azerbaijan shows little sign of easing. Meanwhile, there have been no diplomatic breakthroughs for around a week. 

On Wednesday, Russian President Vladimir Putin told TASS news agency that Russia is doing everything in its power to end the conflict in the South Caucasus as quickly as possible and to save lives. 

(With input from agencies)