Assad's speech on Sunday was billed as the unveiling of a new peace plan but the president offered no concessions and dismissed the prospect of negotiations with Syrian opposition groups, which described it as a renewed declaration of war.
Iran has steadfastly backed Assad's rule since an uprising began almost two years ago and regards him as an important part of the axis of opposition against Israel. Iran describes many Syrian opposition groups as "terrorists" who are backed by Western and Arab states.
"This plan rejects violence and terrorism and any foreign interference in the country and outlines a future for the country ... through a comprehensive political process," Iranian foreign minister Ali Akbar Salehi said in a statement published by state news agency, IRNA.
Salehi urged world and regional powers to support attempts to end the crisis through a "Syrian solution".
The Islamic Republic has sought international backing for its six-point plan to resolve the conflict, which the United Nations says has killed more than 60,000 people. The plan calls for an immediate end to violence and negotiations between all parties to form a transitional government, but does not call for Assad to step down.
Western powers and Syrian opposition groups view Tehran with deep distrust, saying it provides significant military and financial support to the Syrian government.
(Reporting By Marcus George; Editing by Pravin Char)