Syria's President Bashar al-Assad on Tuesday praised Iran's support as a "key pillar" in his fight against rebels, as a third Iranian official visited Damascus in less than a week. The visits come after several military losses for the Syrian government and as Tehran negotiates a key nuclear deal with the United States, which backs the rebels fighting Assad. "The support given by Iran to the Syrian people constitutes a key pillar in the battle against terrorism," official news agency SANA quoted Assad as saying during a meeting with Ali Akbar Velayati, foreign affairs adviser to Iran's supreme leader.