Syria's main Western-backed opposition has threatened to sit out a peace conference this week aimed at ending the country's civil war unless the United Nations retracts its last-minute decision to invite Iran.
The Syrian National Coalition said it would not attend the talks unless the U.N. withdraws the invitation to Iran by 1900 GMT Monday.
France and Saudi Arabia joined the United States in rejecting Iran's participation in the Geneva 2 peace talks - scheduled to open Wednesday in Switzerland - unless Tehran publicly agreed to help to establish a transitional government for Syria with full executive powers.
U.N. Secretary-General Ban Ki-moon said his invitation to Tehran came after he had received assurances from Iran that it had accepted that premise.
The Iranian foreign ministry said Monday it had accepted the invitation "without preconditions."
But the semi-official Fars news agency quoted lawmaker Abbasali Mansouri and a second, unnamed source as saying Iran's participation did not mean it backed a plan for Syria's political transition agreed at a Geneva conference in June 2012.
The United States and its allies say this plan means Syrian President Bashar al-Assad would have to step down.
The U.N. chief told reporters Sunday he believes Iran "needs to be a part of the solution in Syria," and that Iranian Foreign Minister Javad Zarif assured him Iran understands the basis of the talks.
Mr. Assad told the French news agency in an interview published Monday that the conference must focus on terrorism, and that his forces are fighting an extremist group, not a popular uprising.
The Syrian government has routinely classified opposition fighters as terrorists throughout the nearly three-year-old conflict.
AFP quoted Mr. Assad saying some of the opposition groups set to attend the conference were "created" by intelligence agencies in Qatar, Saudi Arabia, France and the United States. Each of those nations is a member of the so-called Friends of Syria, which has supported the opposition.
Mr. Assad also said there is a "significant" chance he will run again for president, and that he will not hesitate to do so if the public supports his candidacy.
Syria has said the issue of Mr. Assad giving up power is not up for discussion at the peace talks, so few experts expect the negotiations will reach this goal. But they say they do hope the discussions will result in increased humanitarian access and local cease-fires to make life easier for Syrian civilians.