Kerry said he spoke in the morning with Russian Foreign Minister Sergey Lavrov to discuss terms of a cease-fire and the two now must reach out to the parties in the conflict.

He declined to go into the details of the agreement, saying it "is not yet done." But he said he hoped President Barack Obama and Russian President Vladimir Putin would talk soon and that after that, implementation could begin.

"The modalities for a cessation of hostilities are now being completed," Kerry said.

The Russian Foreign Ministry seemed to stop short of Kerry's announcement. The ministry said Lavrov and Kerry spoke on the phone Sunday for a second day in a row and discussed "the modality and conditions" for a cease-fire in Syria that would exclude groups that the UN Security Council considers terrorist organisations.

Fighting has intensified in Syria during recent weeks and an earlier deadline to cease military activities was not observed.

The United States, Russia and other world powers agreed on February 12 on a deal calling for the ceasing of hostilities within a week, the delivery of urgently needed aid to besieged areas of Syria and a return to peace talks in Geneva.

Latest News from World News Desk