Azerbaijan's President Ilham Aliyev
Azerbaijan's President Ilham AliyevReuters

The president of Azerbaijan Ilham Aliyev has threatened to resume war against the Armenian "barbarians and vandals" over the disputed enclave of Nagorno-Karabakh through a long Twitter rant.

The worst clashes in years in the 4,400-km sq of disputed territory located within Azerbaijan's current borders left at least 15 soldiers dead in recent days.

The neighbouring countries fought a full-fledged war over the enclave after the collapse of the USSR in the early 1990s that caused at least 30,000 deaths over six years. A ceasefire brokered by Russia in 1994 put an end to hostilities but international attempts to revive the peace process have failed since then.

Nagorno-Karabakh has maintained de facto autonomy. Azerbaijan keeps claiming the land as its own, and considers it an occupied territory, stressing that the self-declared government lacks international recognition.

Employing his utmost belligerent rhetoric, Aliyev declared that "just as we have beaten the Armenians on the political and economic fronts, we are able to defeat them on the battlefield".

Aliyev and his Armenian counterpart, president Serzh Sargsyan, are due to meet in the Russian Black Sea resort of Sochi to discuss a settlement.

Russia said on its website: "We see the events of recent days as a serious violation of agreements on a ceasefire and declared intentions to achieve a regulation through political means.

"We take the position that any further escalation is unacceptable."

The US expressed "concern" about the escalation of violence and remarked that the ceasefire "needs to be respected".