The United States on Thursday called a nationwide ceasefire deal in Syria brokered by Russia and Turkey a "positive development," saying it hoped it would lead to fresh talks on the war-wracked country's political future.

"We hope it will be implemented fully and respected by all parties," State Department spokesman Mark Toner said in a statement, emphasizing that Washington was not part of the ceasefire negotiations.

"Any effort that stops the violence, saves lives, and creates the conditions for renewed and productive political negotiations would be welcome."

Syria's army and Moscow announced the agreement on the ceasefire, to take effect at midnight.