Clashes erupted between troops from Azerbaijan and the rebel Nagorno-Karabakh region on Saturday, the two sides said, disputing who had violated a fragile ceasefire again.

Nagorno-Karabakh's military also said that Armenian anti-aircraft forces downed an Azeri helicopter, although the report was denied by Azerbaijan.

Nagorno-Karabakh, which lies inside Azerbaijan but is controlled by ethnic Armenians, has run its own affairs with heavy military and financial backing from Armenia since a separatist war ended in 1994.

Both sides report numerous casualties, accusing each other on Saturday of violating a ceasefire, a sign that the two-decade-old conflict which has left some 30,000 people dead is far from a peaceful resolution. Similar violence was reported last month.

"The enemy, using tanks, artillery and aviation made attempts to get deep into the defense lines of the Nagorno-Karabakh Army of Defence and capture tactical positions. The enemy was thwarted," the Armenian Defence Ministry said in a statement.

War erupted over Nagorno-Karabakh in 1991 as the Soviet Union broke up, and killed about 30,000 people. A ceasefire was called in 1994 but violence has sporadically broken out since.