The U.S., Russia and France are pressing the leaders of Armenia and Azerbaijan to begin immediate negotiations over a territory dispute that recently sparked the worst violence there in 26 years.

Senior U.S. officials say Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov and French Foreign Minister Jean-Marc Ayrault will bring the two presidents together in Vienna on Monday. They'll urge them to recommit to a 1994 cease-fire and resume stalled peace talks that have dragged on for two decades without visible result.

Nagorno-Karabakh, a region in Azerbaijan, has been under the control of local ethnic Armenian forces and the Armenian military since 1994. The conflict is fueled by long-simmering tensions between Christian Armenians and mostly Muslim Azeris.