U.S. President Barack Obama reiterated his backing for Medvedev's resolve in bringing the two sides in the dispute together after they failed to reach agreement on a framework to end the conflict during a summit last month in the Russian city of Kazan.
Medvedev since then has continued diplomatic efforts to revive the stalled peace process.
A statement released by the White House indicated Obama had a phone conversation Monday with Medvedev which he "expressed his support for President Medvedev's mediation efforts regarding Nagorno-Karabakh."
Obama, the statement said, also pledged U.S. backing "for the effort to reach a framework agreement for negotiating a final peace agreement that will put an end to this conflict."
Armenia and Azerbaijan warred for six years over the Nagorno-Karabakh territory, an Armenian-majority enclave within Azerbaijani borders. The active conflict, which left more than 30,000 dead, ended with a cease-fire in 1994.
The territory has remained under Armenian control since it claimed independence from Azerbaijan but its final status remains unresolved, and tensions over the situation are still high.
The OSCE Parliamentary Assembly Sunday expressed its concerns over the increasing tensions there as part of its Belgrade Declaration, in which it called for more active efforts to resolve the conflicts in Nagorno-Karabakh, Moldova and Georgia.
Obama's remarks reiterated a joint statement he, along with Medvedev and French President Nicolas Sarkozy, made in May at the Deauville summit of the Group of Eight.
That statement was issued in their capacities and the presidents of the three nations leading the Organization for Security and Cooperation in Europe's Minsk Group, which has been seeking a resolution of the conflict since 1995.
It urged the presidents of Armenia and Azerbaijan to "demonstrate their political will" by finalizing the latest version of the basic principles of a framework agreement hammered out in March, asserting, "further delay would only call into question the commitment of the sides to reach an agreement."
But that remains an elusive goal after the Kazan meeting, during which Baku asked to introduce 10 new amendments to the basic principles, Armenian officials said.
Armenian Foreign Minister Edward Nalbandyan said afterward an agreement on Nagorno-Karabakh would be only possible if Azerbaijan gives up some of the amendments it suggested, the Russian news agency RIA Novosti reported.
Shuttle diplomacy has continued since the failure of the Kazan summit. Russian Foreign Minister Sergey Lavrov visited both Yerevan and Baku Friday, bearing letters from Medvedev in which the Russian leader proposed ways to keep the talks moving ahead.
"We want the problem to be solved and solved in a way which will bring ultimate peace and stability to the region," Armenian President Serzh Sargsyan said, indicating his country would study the proposals.
"We are carefully studying the proposal made by President Medvedev, and after a thorough insight we will give our response," Azerbaijani Foreign Minister lmar Mammadyarov added.
Mammadyarov is to make an official visit to Russia next week at Lavrov's invitation, and it is expected both sides will continue the talks on the Nagorno-Karabakh settlement, RIA Novosti reported.