Speaking to Radio Free Europe/ Radio Liberty, Steven Mann, the U.S. co-chairman of the Organization for Security and Co-operation in Europe's Minsk Group, said the two leaders met Sunday for 2 1/2 hours.
There was a good atmosphere in the talks and again, a good atmosphere and a detailed discussion," he told the radio network.
The Minsk Group, led by the United States, Russia, and France, has been negotiating the conflict since 1992.
The enclave has remained a dispute since the predominantly Armenian Nagorno-Karabakh seceded from Azerbaijan in 1988. That set off a six-year war before a truce was called. Officially, the countries are still at war.