Russian Foreign Minister Sergei Lavrov said that UN secretary-general Ban Ki Moon's U-turn on inviting Iran to Syria peace talks was regrettable but "no catastrophe."

Mr Ban bowed to US pressure late on Monday and withdrew an invitation to Iran to join this week's peace talks in Switzerland.

Mr Lavrov said Mr Ban's decision to withdraw Iran's last-minute invitation to attend the Montreaux conference would have a negative impact.

"This story hasn't helped strengthen UN authority," he said, adding that recalling the offer looked "unseemly" and warning that spurning Iran would deepen divisions in the Islamic world.

"The absence of Iran isn't going to help strengthen the unity of the world's Muslims," he said.

He reaffirmed Russia's stance that the presence of Iran was essential for the success of the talks.

The invitation to Iran extended by Mr Ban on Sunday had put the talks in jeopardy, with the US pushing for the offer to be rescinded and the Syrian opposition threatening to skip the event entirely.

Mr Lavrov insisted: "There is no catastrophe. We will push for a direct dialogue between the Syrian parties without any preconditions."

Iran also criticised the UN chief's decision, calling the diplomatic about-face "deplorable."

Foreign Ministry spokeswoman Marzieh Afkham said the decision to withdraw the invitation showed the UN chief came "under some pressure."

She said: "From our point of view, the withdrawal is deplorable."

Ms Afkham added that Iran would expect Mr Ban to explain the "real reasons" for withdrawing the invitation.

The opposition Syrian National Coalition hailed the withdrawal as a victory and said it would now attend the talks "in which killers and criminals do not participate."

The coalition had issued an ultimatum that Iran must commit publicly within hours to remove its "troops and militias" from Syria.

The withdrawal cleared the way for the conference to open today as planned in Montreux, with high-ranking delegations from the US, Russia and close to 40 other countries attending.

Face-to-face negotiations between the Syrian government and the rebels are to start on Friday in Geneva.