US Secretary of State Hillary Clinton and Russian Foreign Minister Sergei Lavrov have agreed they needed to work together on Syria, a US official said.

"Her message to him was: 'we've got to start working together to help the Syrians with Syria's political transition strategy. And I want our people to work together on ideas in Moscow, Europe, in Washington, wherever we need to'," the official said, following a phone conversation between Clinton and Lavrov.