Azerbaijan has said at least 12 people have died after shelling levelled a row of homes in the city of Ganja, with 40 more wounded in a sharp escalation of the conflict with Armenia over the region of Nagorno-Karabakh.

The Azeri prosecutor general’s office said that two shells hit apartment buildings in the country’s second largest city. There has been no official reaction from Armenia as yet.

The attack on Saturday, which saw a second strike in another part of Ganja and a third reach the nearby strategic city of Mingecevir, came hours after Azerbaijani forces shelled the ethic Armenian separatist region’s capital, Stepanakert.

The spike in violence further undermines international efforts to calm a resurgence of fighting between Christian Armenians and Muslim Azerbaijanis before it draws in regional powers Russia and Turkey.

Reporters in Ganja saw rows of houses turned to rubble by the shelling, and a rescue team remove black bags containing body parts from the scene. The strike shattered the walls and ripped the roofs off buildings in the surrounding streets.