Iran did not "announce officially and openly its agreement (to)... the creation of a transitional government," said a Saudi official statement.
This renders that the Islamic Republic is "unqualified to attend" the international peace conference on Syria that opens Wednesday in Switzerland, it claimed.
UN Secretary General Ban Ki-moon sparked a furor Sunday by inviting Iran to the talks.
Ban's invitation came after Tehran vowed to play a "very positive and constructive role" in efforts to end Syria's three-year civil war.
Iran said Monday that it will attend the peace talks but without preconditions.
Washington, London and Paris reacted immediately, saying Iran would have to clearly and publicly support the idea of a Syrian transitional government if it wanted to attend.
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 Saudi statement said of this week's conference that "its main role is to implement Geneva I."
Saudi Arabia and some other Arab regimes of the Persian Gulf have repeatedly voiced support for extremist groups fighting Assad's government.
Saudi Arabia's intelligence chief Bandar bin Sultan told Russian President Vladimir Putin last month that Riyadh would send a delegation to the meeting, but only on the condition the militant groups are represented by its Saudi-backed National Coalition.
On November 4, Syrian Information Minister Omran al-Zoubi said Saudi Arabia is responsible for the death and destruction throughout the Islamic world today, including in Syria, calling on Riyadh to stop its policy of sponsoring terrorism in regional states.
NJF/NJF