U.S. Secretary of State John Kerry has expressed "strong concern" to the leaders of Armenia and Azerbaijan over recent violence around the disputed Nagorno-Karabakh region.
Kerry met with Armenian President Serzh Sarkisian and Azerbaijani Presidentt Ilham Aliyev on the sidelines of a NATO summit in Wales.
They discussed efforts to resolve the conflict over Nagorno-Karabakh after "the deadliest period in the conflict since the 1994 cease-fire took effect," a State Department statement said.
Exchanges of gunfire early last month killed more than 20 people.
Azerbaijan claims Nagorno-Karabakh as part of its territory, but the region has been occupied and administered by pro-Armenian forces for some 20 years.
Kerry urged both sides to respect the cease-fire, which has frequently been violated, and to work with the Minsk Group of the Organization for Security and Cooperation in Europe to resolve the conflict.