Armenian and Azerbaijani troops have clashed in the heaviest fighting in months over the disputed Nagorny Karabakh region, leaving at least four Armenian soldiers dead, officials said yesterday.

With tensions rising between the two rival nations, Armenia's defence ministry said in a statement that four soldiers had been killed and four wounded after Azerbaijani forces attacked separatist positions late Friday.

The ministry also claimed that an Azerbaijani soldier had been killed.

Azerbaijani Defence Ministry spokesman Eldar Sabiroglu confirmed the fighting had taken place but blamed Armenian forces for the attack and said Yerevan was understating its losses.

"Armenian armed forces breached the ceasefire. They have lost even more soldiers than they admit," he told AFP. He refused to comment on casualties among Azerbaijani soldiers.

Armenian President Serzh Sarkisian condemned the incident as a "cowardly provocation", noting that it occurred almost immediately after he met with Azerbaijani President Ilham Aliyev for talks in St Petersburg last Thursday under the mediation of Russian President Dmitry Medvedev.

"Provocations are unacceptable, and the recent cowardly provocation is even more unacceptable as it came just hours after the meeting held under Russia's mediation," Sarkisian said in a statement.

Tensions over Karabakh have risen in recent months amid stalled negotiations over the status of the region, where ethnic Armenian separatists backed by Yerevan seized control from Baku in a war in the early 1990s that claimed an estimated 30,000 lives.