ISTANBUL (Reuters) - Turkish Prime Minister Tayyip Erdogan said on Thursday he was doubtful that President Bashar al-Assad would fulfill his pledge to put Syria's chemical weapons under international control, and said he was buying time for new "massacres".

"The Assad regime has not lived up to any of its pledges, it has won time for new massacres and continues to do so," Erdogan said in a speech in Istanbul. "We are doubtful that the promises regarding chemical weapons will be met."

Assad's government says it has accepted a Russian plan to surrender Syria's chemical weapons to international control to try to win a possible reprieve from a U.S. military strike.

(Writing by Daren Butler; Editing by Nick Tattersall and Kevin Liffey)