BAKU, Azerbaijan (AP) -- Heavy fighting erupted Saturday between Armenian and Azerbaijani forces over the separatist region of Nagorno-Karabakh. Azerbaijan said 12 of its soldiers were killed and claimed to have inflicted heavy casualties on the Armenian forces.
The fighting was one of the worst outbreaks since the 1994 end of full-scale war over the region. Since 1994, mountainous Nagorno-Karabakh has been under the control of local ethnic Armenian forces and the Armenian military.
Armenian forces also occupy several areas outside Nagorno-Karabakh proper. The sides are separated by a demilitarized buffer zone, but small clashes have broken out frequently.
Each side blamed the other for Saturday's escalation.
In a statement, Azerbaijan's Defense Ministry said 12 of its soldiers "became shahids" — Muslim martyrs — and said one of its helicopters was shot down.
The statement also claimed that more than 100 Armenian forces were killed or wounded and that six tanks and 15 artillery positions were destroyed.
Armenia in turn claimed to have inflicted heavy damage on Azerbaijani forces, but did not immediately give figures.
Nagorno-Karabakh, a region in Azerbaijan, has been under the control of local ethnic Armenian forces and the Armenian military since 1994.
David Babayan, a spokesman for Nagorno-Karabakh's separatist president, said a boy of about 12 was killed and two other children were wounded in a Grad missile barrage by Azerbaijani forces. He characterized the fighting as the worst since 1994.
Russian President Vladimir Putin urged all sides to cease firing and "show restraint," Kremlin spokesman Dmitry Peskov was quoted as saying by Russian news agencies. Russia's foreign and defense ministers contacted their Azerbaijani and Armenian counterparts in hopes of stabilizing the situation, the ministries said.
"The situation along the entire length of the line of opposition between Karabakhi and Azerbaijani armed forces continues to be extremely difficult," Armenian defense ministry spokesman Artsrun Hovhannisyan told The Associated Press.
Years of negotiations under the Organization for Security and Cooperation in Europe have brought little progress in resolving the territorial dispute.
Armenian forces also occupy several areas outside Nagorno-Karabakh. The sides are separated by a demilitarized buffer zone, but both claim frequent violations by the other.
The Armenian Defense Ministry said Azerbaijan used aircraft, tanks and artillery to try to make inroads into Nagorno-Karabkh and that "Azerbaijani authorities bear all responsibility for the unprecedentedly supercharged situation."
The Azerbaijani Defense Ministry said the fighting began when Armenian forces fired mortars and large-caliber artillery shells across the front line. Ministry spokesman Vagif Dargyakhly told The Associated Press that more than 120 shots were fired, some of which hit civilian residential areas.