BAKU/YEREVAN (Reuters) - Azerbaijan said on Tuesday that forces backed by neighbor Armenia had killed two of its soldiers near the disputed territory of Nagorno-Karabakh, which was the cause of a war that killed about 30,000 people in the early 1990s.

The conflict between ethnic Azeris and Armenians erupted in 1991 over the area, a mountainous enclave within Azerbaijan but with a majority Armenian population, which Armenian-backed forces seized along with seven surrounding Azeri districts.

A truce was signed in 1994, but there was no peace treaty. Violence still flares sporadically along the ceasefire line and Azerbaijan's border with Armenia - underlining the risk of a conflict in the South Caucasus, a transit route for oil and gas to Europe and a region where Turkey, Russia and Iran have interests.

Nagorno-Karabakh, home to about 160,000 people, has run its own affairs with heavy Armenian military and financial backing since the war.

"A soldier and an officer of Azeri army died on the frontline today as a result of a violation of the ceasefire agreement from the Armenian side," said Azeri Defense Ministry spokesman Teimur Abdullayev, referring to ethnic Armenians in Nagorno-Karabakh.

Authorities in Nagorno-Karabakh denied any involvement in the incident.

"This is again disinformation on the part of the Azeri side, whose representatives are trying to convince the international community that the army of Nagorno-Karabakh is violating the ceasefire agreement," said Senor Hasratyan, the enclave's army spokesman.

Armenia has a policy of not commenting on incidents on the frontline in the dispute that has resisted almost two decades of mediation by envoys from the United States, France and Russia.

Oil-producing Azerbaijan, host to global majors including BP, Chevron and ExxonMobil, frequently threatens to take the mountain enclave back by force, and is spending heavily on its armed forces.

Armenia says it would not stand by if the enclave were attacked and any war could spread if pipelines carrying Azeri oil and gas to Europe via Turkey, or Armenia's nuclear power plant, were hit.

Armenia has a collective security agreement with Russia, while Azerbaijan has one with Turkey.

(Reporting by Lada Evgrashina in Baku and Hasmik Mkrtchyan in Yerevan; Writing by Margarita Antidze; Editing by Gabriela Baczynska and Pravin Char)