The Kremlin says Russian President Vladimir Putin and Iranian President Hassan Rohani agreed in a December 31 telephone call to coordinate closely on bringing an end to the war in Syria.
In a December 31 statement, the Kremlin said the two leaders agreed on the importance of a new cease-fire deal brokered by Russia and Turkey and plans to launch peace negotiations between the Syrian government and the armed opposition in Astana, the capital of Kazakhstan.
"It was agreed to continue the close coordination of efforts with the goal of reaching a final resolution to the Syria crisis," the Kremlin statement said.
Both Moscow and Tehran are backing Syrian President Bashar al-Assad in the conflict.
Meanwhile, sporadic fighting continued in parts of Syria on December 31 despite a cease-fire deal that took hold a day earlier, as rebel groups accused government forces of "continued violations" and warned that the truce could be voided.
Activists and monitors said Assad's forces have been pushing forward on a number of fronts following the cease-fire brokered by Turkey and Russia.
The Syrian Observatory for Human Rights, a Britain-based monitor, said the truce remained largely intact. But several rebel groups said in a statement that "continued violations" by Assad's forces and attacks on "areas under the control of the revolutionary factions will make the agreement null and void."
The warning came ahead of a UN Security Council meeting scheduled later on December 31 to vote on a resolution endorsing the truce and a peace effort that would include a transitional government for Syria.
The government and the opposition have blamed one another for cease-fire violations. Russia, which is backing Assad in the conflict, accused the rebels on December 30 of violating the truce a dozen times in a 24-hour span.