DUBAI (Reuters) - Iranian Foreign Minister Mohammad Javad Zarif said on Thursday the Syrian government could not have been behind a possible chemical weapon attack on the outskirts of Damascus as President Bashar al-Assad's forces had the upper hand in the fighting.

"If the use of chemical weapons is true, it has definitely been carried out by terrorist ... groups, because they have proved in action that they refrain from no crime," Iran's Press TV quoted Zarif as telling his Turkish counterpart, Ahmet Davutoglu, in a telephone conversation.

(Reporting by Jon Hemming; Editing by John Stonestreet)