At the same time the Russian Foreign Minister Sergei Lavrov downplayed the move, saying the conference in the Swiss town of Montreux on Wednesday was a "one-day event".

"Of course this is a mistake," Lavrov told reporters on Tuesday. "But no disaster has happened," he added.

"In any case we are talking about a one-day event on January 22 to which some 40 foreign ministers of various states including from the most remote regions have been invited."

"Of course, despite the largely ceremonial nature of this event, Iran's absence from a list of 40 states cannot but cause questions."

"The symbolism is still important," he added.

"I am just sorry that this whole story did not boost the authority of the United Nations."

In an abrupt reversal, the UN barred Iran Monday from the peace conference after it refused to back calls for a transitional government to end the three-year war in Syria.

The unprecedented diplomatic action averted a Syrian opposition boycott of the talks.

But a key bloc in the opposition coalition broke away in protest at the proposed talks with President Bashar al-Assad's representatives.

"The Syrian crisis has laid bare the contradictions that have accumulated in the region including within the Muslim world," said Lavrov.

BA/BA