Less than 24 hours after he surprised many in the international community with the initial invitation, U.N. Secretary general Ban Ki-moon disinvited Iran on Tuesday from this week's peace conference on the Syrian civil war.

Iran, Syria's most important regional ally, called the withdrawal "deplorable," and Russia, another Syrian backer, said the move was a "mistake" but not a "catastrophe."

Ban withdrew the invitation under intense pressure from the U.S. Secretary of State John Kerry, who, according to the New York Times, was furious when he learned of the initial invite.

The U.N. also said Iran backed out of a previous agreement to adhere to a specific mandate. Iran disagreed, placing full blame for the move on Ban succumbing to U.S. criticism.

"I made it clear in numerous phone conversations with the secretary general that Iran does not accept any preconditions to attend the talks," [Iranian Foreign Minister Mohammad Javad] Zarif said, according to the ISNA news agency.

"It is also regrettable that Mr. Ban does not have the courage to provide the real reasons for the withdrawal," Mr. Zarif said, adding that "Iran was not too keen on attending in the first place."

On Sunday, Ban said Iran's presence on the conference was necessary for any significant changes in the Syrian civil war, which so far has killed an estimated 100,000 civilians. But on Tuesday, he said he "is deeply disappointed by Iranian public statements today that are not at all consistent with that stated commitment," and added that Iran was not welcome at the conference.

The peace talks begin on Wednesday in Switzerland, with representatives from 30 countries gathering to help in negotiations between Syrian President Bashar al-Assad and the rebels attempting to overthrow his government. Assad, though, seems unwilling to step down. "I see no reason why I shouldn't stand," he told the AFP of Syrian presidential elections in June. "In short, we can say that the chances for my candidacy are significant."

[Image via AP]