"Based on the official invitation, Iran will participate in this conference without any preconditions," Afkham was quoted as saying by the official IRNA news agency.
UN Secretary General Ban Ki-moon sparked a furore yesterday by inviting Iran to the so-called Geneva II peace talks.
Ban's invitation came after Tehran vowed to play a "very positive and constructive role" in efforts to end Syria's worsening three-year civil war that the UN says has claimed well over 100,000 lives.
Iran is a key backer of Syrian President Bashar al-Assad.
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Western powers have so far opposed Iran's presence on the grounds that Tehran had not accepted an initial communique adopted by major powers in Geneva in June 2012 calling for the creation of an interim government.
Iran has strongly resisted pressure to accept the communique.
"The previous agreements which were in line with the interests of foreign powers and reactionary (groups) in the region cannot be the basis for the next negotiations," Fars news agency quoted Iran's top military commander Brigadier General Masoud Jazayeri as saying.