Russia's foreign minister says that the U.N. decision to rescind the invitation to Iran to join this week's Syria peace talks was a mistake but not a catastrophe.

Sergey Lavrov said Tuesday that United Nations Secretary General Ban Ki-moon's decision to withdraw his last-minute offer to Iran to attend the conference would have a negative impact on the United Nations image.

Lavrov, speaking at a news conference, reaffirmed Russia's argument that the presence of Iran was essential for the success of the conference that is set to begin Wednesday in the Swiss resort of Montreux.

Iran has been the main regional ally of Syrian President Bashar Assad, supporting his regime with advisers, money and materiel since the uprising began in 2011.