BEIRUT (Reuters) - Syrian government forces will advance soon to take Raqqa city, which U.S.-backed fighters seized from Islamic State last month, a senior Iranian official said on Friday.  Ali Akbar Velayati, the top adviser to Iran s Supreme Leader, also accused the United States of seeking to divide Syria by stationing its forces east of the Euphrates river.   We will witness in the near future the advance of government and popular forces in Syria and east of the Euphrates, and the liberation of Raqqa city,  he said in televised comments on a visit to Beirut.  Since early in the Syrian war, Iran has provided critical military support to the Damascus government, helping it regain swathes of land from rebels and militants. Last month, U.S.-backed militias declared victory in Raqqa, Islamic State s former headquarters in Syria, after months of fighting with the help of the U.S.-led coalition.  The Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab militias, is also battling Islamic State in eastern Syria with U.S.-led air strikes and special forces. The SDF assault in Deir al-Zor has focused on territory east of the river, which bisects the oil-rich province.     The Syrian army, with Russian air power and Iran-backed militias, is waging its own separate offensive against Islamic State there, mostly to the west of the river. The U.S.-led coalition and the Russian military have been holding  deconfliction  meetings - to prevent clashes between planes and troops - though the two offensives have sometimes come into conflict. The U.S.-led coalition against Islamic State has repeatedly said it does not seek to fight Syrian President Bashar al-Assad s military.  After capturing Raqqa, the SDF said the people of the majority Arab city would decide their own future  within the framework of a decentralized, federal, democratic Syria.   The Kurdish-led SDF pledged  to protect the frontiers of (Raqqa) province against all external threats  and to hand control to a civil council from the city. But last week, Damascus said it deemed Raqqa  occupied  until the Syrian army took control. With Islamic State near defeat in Syria, rivalry between Damascus and Kurdish-led forces is emerging as a fault line that could draw the United States in more deeply and complicate Russian diplomacy. Syria s main Kurdish groups hope for a new phase of negotiations to shore up their autonomous regions in the north. The Syrian government, however, has asserted in more forceful terms its claim to territory under SDF control including oil fields in the east.  