* Clashes highlight risk of wider conflict in Caucasus region
* OSCE warns against further escalation of conflict
By Hasmik Mkrtchyan and Nailia Bagirova
YEREVAN/BAKU, Aug 3 (Reuters) - Armenia and Azerbaijan accused each other on Sunday of escalating tensions near the disputed territory of Nagorno-Karabakh, leading to violent clashes and at least 15 soldiers killed.
The clashes in recent days highlighted the risk of broader conflict around Nagorno-Karabakh, a mountainous enclave of Azerbaijan with a majority ethnic Armenian population, and the wider South Caucasus area where vital oil and natural gas flow from the Caspian region to Europe.
The Organisation of Security and Cooperation in Europe (OSCE) issued a statement on Saturday warning against further escalation.
An Azeri foreign ministry statement accused Armenia of provoking "a substantial escalation along the frontline" and causing casualties. "The whole responsibility is on official Yerevan, which gives orders to such a provocative steps," it said.
For its part, Armenia accused Azerbaijan of raising tensions and then blaming it. Both are former Soviet republics.
"Rejecting the proposals of the international community on the establishment of a mechanism of investigation of incidents, Azerbaijan is assuming the whole responsibility for the ceasefire violations," Foreign Minister Edward Nalbandian said in a statement.
Energy-producing Azerbaijan, host to oil majors including BP , Chevron and ExxonMobil, frequently threatens to take Nagorno-Karabakh back by force and is spending heavily on its armed forces.
Fighting between ethnic Azeris and Armenians first erupted in 1991 and a ceasefire was called in 1994. But Azerbaijan and Armenia have regularly traded accusations of further violence around Nagorno-Karabakh and along the Azeri-Armenian border.
Nagorno-Karabakh runs its own affairs with heavy military and financial backing from Armenia since the war that killed about 30,000 people two decades ago. Armenian-backed forces also seized seven Azeri districts surrounding Nagorno-Karabakh.
Efforts to reach a permanent settlement of the Nagorno-Karabakh conflict have failed despite mediation led by France, Russia and the United States.
The OSCE has expressed concern about the intense upsurge in violence along the frontline that has resulted in casualties among Azeri soldiers and ethnic Armenian separatists.
OSCE officials have also said they were deeply concerned about shooting at a clearly marked International Committee of the Red Cross (ICRC) vehicle while it was assisting the local population on the Armenian-Azeri border.
They strongly condemned the deliberate targeting of civilians and shooting at representatives of international organisations.
"Retaliation and further violence will only make it more difficult to continue efforts to bring about a lasting peace," the OSCE head and the co-chairs of the OSCE Minsk group said in a statement on Saturday. (Writing by Margarita Antidze; Editing by Tom Heneghan)