A turmoil erupted after Iran, a major backer of Syrian President Bashar al-Assad, was invited on Sunday to the Montreux meeting, scheduled for Wednesday and a prelude to actual talks planned for Friday between the Syrian government and opposition delegations.
Several countries objected to Iran's participation, but Ban said he had been assured orally of Iran's acceptance of the Geneva Communique. Then, earlier on Monday, an Iranian foreign ministry spokeswoman did not articulate that agreement.
Ban's spokesman Martin Nesirky said at a regular mid-day briefing that because of the developments Ban was "urgently considering his options", indicating that the session could be in jeopardy.
In late afternoon, Nesirky read a statement to reporters saying the conference would go-ahead without Iran.
"The secretary-general is deeply disappointed by Iranian public statements today that are not at all consistent with that stated commitment," Nesirky said.
"He continues to urge Iran to join the global consensus behind the Geneva Communique. Given that it has chosen to remain outside that basic understanding, he has decided that the one-day Montreux gathering will proceed without Iran's participation."