Iran's President Hassan Rouhani Wednesday slammed the participation of "supporters of terrorists" in Syria peace talks, saying this endangered the chances of the conference succeeding, Mehr news agency reported.
"All the signs show that we cannot have much hope that the Geneva II conference will find a solution to the problems of the Syrian people and the fight against terrorism," Rouhani said before leaving for the World Economic Forum in the Swiss resort of Davos.
"We also don't have much hope that this conference will be efficient in establishing stability since some supporters of the terrorists are participating in it," he added.
Syria's regime refers to rebels fighting to topple President Bashar al-Assad's regime as "terrorist groups" taking orders from foreign states.
Tehran has staunchly supported Assad's government during the conflict that began in 2011 and is estimated to have killed more than 130,000 people.
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The United Nations abruptly withdrew Tehran's invitation to Wednesday's peace talks in the Swiss town of Montreux over its refusal to back calls for a transitional government to end the conflict.
Iran refuses to consent to a transitional government in Syria, which was agreed at a first international Geneva gathering in June 2012.
Iranian participation in the talks was one of the thorniest issues in the build-up to Wednesday's talks, the most intense diplomatic bid yet to end the conflict.
Russia, a Damascus ally and co-initiator of the talks, had urged that Iran be involved in the process, with Foreign Minister Sergei Lavrov calling Tehran's exclusion a "mistake".
The United States, the other architect, along with Britain and France wants Iran to sign up to the communique issued after the first Geneva meeting, which called for a transitional administration to replace Assad.