Yerevan (dpa) - Heavy fighting was reported in the disputed region Nagorno-Karabakh on Tuesday, despite international appeals to return to an agreed ceasefire.

Armenia and Azerbaijan accused each other of heavy shelling in the landlocked region in the southern Caucuses which they both claim as their territory.

Authorities in Nagorno-Karabakh reported rocket and artillery fire from the Azeri side.

The Azeri Ministry of Defence accused Armenia of shooting first and shelling the Terter region, among others.

"This is a complete lie. Azerbaijan is preparing the ground for aggressive action against peaceful locations," a spokesperson of the Armenian Defence Ministry said. She added Azerbaijan was attacking on all fronts.

Nagorno-Karabakh is controlled by Armenia but recognized by the United Nations as part of predominantly Muslim Azerbaijan.

Authorities in Nagorno-Karabakh said the number of civilian casualties rose to 31, while 525 soldiers were killed in the fighting.

Azerbaijan has not disclosed its casualties, though many civilians have died.

Armenian Prime Minister Nikol Pashinyan said the ceasefire, which came into force on Saturday under mediation by Russia but was violated on the same day, has not held.

Russian Foreign Minister Sergei Lavrov had urged both ex-Soviet republics to stick to the agreement.

The current conflict has been simmering since the collapse of the Soviet Union in 1990, when the region, predominantly populated by Christian Armenians, broke away from Azerbaijan.

Although there have been repeated outbreaks of violence in recent years, the current flare-up that erupted last month has been the fiercest since a ceasefire in 1994.