Deadly clashes erupted between troops from Azerbaijan and the breakaway Nagorno-Karabakh region on Tuesday, the two sides said, giving conflicting casualty tolls and disputing who was to blame.
Violence has intensified this year around Nagorno-Karabakh, which has an ethnic Armenian majority, underlining the risk of broader conflict in the South Caucasus region.
Azerbaijan's Defense Ministry said five Armenian soldiers were killed and about 10 wounded on Tuesday. It said the Armenians were the first to open fire and there were no Azeri casualties.
Nagorno-Karabakh's Defense Ministry, meanwhile, said at least one Azeri soldier was killed and several wounded, while there were no Armenian casualties.
"Information circulated by the Azeri side is just disinformation aimed at hiding its own casualties," it said in a statement.
War erupted over Nagorno-Karabakh in 1991 as the Soviet Union broke up, and killed about 30,000 people. A cease-fire was called in 1994 but violence has sporadically broken out since.
Nagorno-Karabakh has run its own affairs with heavy military and financial backing from Armenia since the war. Armenian-backed forces hold seven Azeri districts surrounding Nagorno-Karabakh.
Efforts to reach a permanent settlement have failed despite mediation led by France, Russia and the United States.
The South Caucasus region is criss-crossed by major oil and gas pipelines. Oil-producing Azerbaijan, host to global majors including BP, Chevron and ExxonMobil, frequently threatens to take Nagorno-Karabakh back by force, and is spending heavily on its armed forces.
Armenia, an ally of Russia, says it would not stand by if Nagorno-Karabakh were attacked.