The leaders of Azerbaijan and Armenia on Friday discussed settlement of the longstanding Upper Karabakh conflict, in a meeting organized by the Organization of Security and Co-operation in Europe (OSCE) Minsk Group.

"(Azerbaijan) President Ilham Aliyev @presidentaz had tete-a-tete meeting with Prime Minister of Armenia Nikol Pashinian in Vienna. Now meeting continues with the participation of OSCE Minsk Group co-chairs," Hikmet Hajiyev, a top foreign policy aide to Azerbaijan's presidency, wrote on Twitter.

"Azerbaijan supports negotiated resolution of conflict within existing format based on (U.N. Security Council Resolution, Helsinki Final Act), principles of international law."

After the closed-door meeting, the leaders were expected to separately meet Austrian Prime Minister Sebastian Kurz.

Azerbaijani Foreign Minister Elmar Mammadyarov met his Armenian counterpart, Zohrab Mnatsakanyan, Thursday in Vienna to discuss Upper Karabakh under Minsk Group mediation, according to Azerbaijan's Foreign Ministry.

The Minsk group -- co-chaired by France, Russia and the U.S. -- was formed to find a peaceful solution to the conflict.

Pashinian, a former journalist, became Armenia's new prime minister last May.

Karabakh-a disputed territory between Azerbaijan and Armenia-broke away from Azerbaijan in 1991 with military support from neighboring Armenia, and a peace process has yet to be implemented.

Three U.N. Security Council resolutions (853, 874 and 884) and U.N. General Assembly resolutions 19/13 and 57/298 refer to Karabakh as being part of Azerbaijan.

The Parliamentary Assembly of the Council of Europe refers to the region as being occupied by Armenian forces.

The Armenian occupation of Karabakh led to the closing of the frontier with Turkey, which sides with Baku in the drawn-out dispute.

Political ties between Ankara and Yerevan remain frozen owing to the Karabakh conflict as well as the legacy of killings during the World War I, which the Armenian diaspora and government describe as "genocide" — a description which Turkey refutes.

Turkey reiterates that the dispute needs to be resolved within the framework of international law and Azerbaijan's sovereignty and territorial integrity.