YEREVAN (Reuters) - Armenian-backed separatists said on Friday three of their soldiers were killed by Azeri forces along the boundary with the breakaway Nagorno-Karabakh region.

Clashes over control of the region, which lies inside Azerbaijan but is controlled by ethnic Armenians, have stoked fears of a wider conflict breaking out in the South Caucasus, which is criss-crossed by oil and gas pipelines.

Nagorno-Karabakh’s self-declared defense ministry said Azeri forces had violated the ceasefire agreement and used anti-tank weapons against one of their block-posts.

The Azeri defense ministry did not comment on the report.

Fighting between ethnic Azeris and Armenians erupted in 1991 and a ceasefire was agreed in 1994. But Azerbaijan and Armenia regularly accuse each other of carrying out attacks around Nagorno-Karabakh and along the Azeri-Armenian border.

Clashes over control of the disputed region have intensified in the past three years and at least 200 people were killed in a violent flare-up last April.

Since mid-January this year, incidents involving heavy artillery and anti-tank weapons have occurred with a significant increase in May when self-guided rockets and missiles were reported to have been used near densely populated areas along the contact line.