Armenia's President Serzh Sarksyan accused Azerbaijan on Friday of threatening a new war over the disputed region of Nagorno-Karabakh.
Here is a look at the background to the conflict the Nagorno-Karabakh region.
* The status of Nagorno-Karabakh or "mountainous Karabakh", has been disputed since the end of World War One, when Armenia and Azerbaijan became independent from the Russian empire. Soviet rule was imposed in the South Caucasus in 1923, and predominantly Armenian-populated Nagorno-Karabakh became an autonomous region within the Azeri Soviet republic.
* In 1988, the Nagorno-Karabakh authorities demanded to be transferred to the Armenian republic. The region declared independence in late 1991, after tensions between Azeris and Armenians living there erupted into war with the break-up of the Soviet Union and independence for Armenia and Azerbaijan.
* Ethnic Armenian forces, backed by Armenia, drove back Azeri forces and took control of seven districts of Azerbaijan adjacent to Nagorno-Karabakh. About 30,000 people were killed in fighting and hundreds of thousands, mostly Azeris, were driven from their homes. A ceasefire has been in place since 1994, but sporadic violence still flares along Azerbaijan's border with Armenia and a line of contact with Nagorno-Karabakh.
* In December 2006, a referendum in Nagorno-Karabakh approved a new pro-independence constitution by a huge majority. Azerbaijan has declared the referendum illegal under international law. The region runs its own affairs with the backing of Armenia, but has no international recognition as an independent state.
* In November 2008 Armenian President Serzh Sarksyan and his Azeri counterpart, Ilham Aliyev, pledged to intensify efforts toward a resolution. Russia, France and the United States have led years of mediation under the auspices of the Organisation for Security and Cooperation in Europe. Baku and Yerevan failed to agree at talks in June 2011 and the angry rhetoric between them has worsened since then. The two have accused each other of triggering recent cross-border clashes prompting worries of a resumption of fighting in the region criss-crossed by energy pipelines to Europe.
* Armenia pulled out of the Eurovision song contest which was hosted by Azerbaijan in May 2012, underscoring tensions. New clashes resulted in nine deaths in June.
* Last August, Azerbaijan pardoned and freed a soldier convicted of killing an Armenian soldier with an axe in Budapest, drawing furious protests from Armenia. Armenia suspended diplomatic relations with Hungary for sending Ramil Safarov back to Azerbaijan after he had served eight years of a life sentence for the murder.