Peace talks aimed at healing rifts from the Russia-Georgia war broke down when the delegations from Russia and Georgia's two separatist provinces refused to take part, mediators said.

"The co-chairs strongly regret the walkout by the Russian participants at the beginning of the fifth session of the Geneva discussions today," said a statement by the United Nations, the European Union and the Organization for Security and Cooperation in Europe.

The round of talks scheduled for Monday and Tuesday was supposed to be the first meeting since February between Georgia, Russia and Russia's allies from the breakaway Georgian regions of Abkhazia and South Ossetia.

The mediators said the Abkhazian delegation refused to attend the talks. The South Ossetians, who came for the beginning, then walked out, followed by the Russians.

"This was all the more regrettable as today's discussions were precisely meant to offer an opportunity to listen to the views of all participants on all security-related and humanitarian questions," said the mediators' statement.

The talks have been held periodically since they began in October to try to heal disputes left over from the war in August between Russia and Georgia.

The mediators urged all parties to attend the talks Tuesday.

"The Geneva Discussions provide the only forum where all participants can engage with one another on the key issues of security and stability as well as humanitarian questions," the mediators said.

Russian Deputy Foreign Minister Grigory Karasin told Russian Channel One television as he was leaving, "We can't discuss the issue of security in Abkhazia and South Ossetia without the Abkhazians and South Ossetians." But Karasin said he hoped talks would resume on Tuesday and that Russia had simply "offered to stop the clock."

Matthew J. Bryza, U.S. deputy assistant secretary of state who attended the fourth round of talks in February, said the two sides agreed on a nonbinding proposal for international observers to regularly discuss ways to diffuse tensions, but accomplished little else.

Bryza said a solution needs to be found to allow Russia and Georgia to address security questions without being seen to give ground on the status of the two separatist republics.