Iran rejects any conditions for taking part in a long-delayed peace conference on Syria, Iranian media reported, in effect dismissing a U.S. suggestion that Tehran back a call for a transitional government in Damascus.

The United States accuses Iran of supporting the government of Syrian President Bashar al-Assad in a civil war that has run for more than two years, killed more than 100,000 people and eluded all efforts at a peaceful settlement.

The U.S. State Department said on Monday Washington would be more open to Iran taking part in a "Geneva 2" conference seeking an end to the war if Iran publicly supported a 2012 statement calling for a transitional authority to rule Syria.

But Iran rejected any conditions being placed on it to participate in diplomatic efforts on Syria, Foreign Ministry spokeswoman Marzieh Afkham said on Tuesday evening.