Deputy Foreign Minister Abbas Araqchi's comments to state television came a day after the United Nations abruptly withdrew Tehran's invitation to Wednesday's conference over its refusal to back calls for a transitional government to end the war in Syria.
"It is clear that a comprehensive solution to the Syria issue will not be found when all influential parties are not involved in the process," Araqchi said.
"Everyone knows that without Iran the chances of a real solution to Syria are not that great."
Tehran is accused of providing military and financial support to Damascus.
It staunchly backs the government of embattled President Bashar al-Assad during the conflict that began in 2011 and is estimated to have killed more than 130,000 people.
Iranian participation in the peace talks has long been a thorny issue in preparations for the forum dubbed Geneva II and due to begin tomorrow in the Swiss town of Montreux.
Russia, a Damascus ally and co-initiator of the talks, has urged that Iran be involved in the process.
But the United States, the other architect, wants Tehran to sign up to the communique issued after the first Geneva meeting in June 2012, which called for a transitional government to replace Assad.
"We were ready to participate in the Geneva II conference and do our part, but we will not accept a precondition that would narrow the solution within set parameters," Araqchi said.


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