MOSCOW — Iran and Russia criticized the UN Tuesday for its decision to rescind its invitation to Iran to join this week’s Syria peace talk in Geneva.

Foreign Ministry spokeswoman Marzieh Afkham said on Tuesday that Ban Ki-moon’s decision to withdraw his last-minute offer to Iran to attend the conference shows the UN chief came “under some pressure,” referring to threats from the main Syrian opposition party to boycott the talks and pressure from the US.

“From our point of view, the withdrawal is deplorable,” she said, adding that Iran would expect Ban Ki-moon to explain the “real reasons” for withdrawing the invitation.

Speaking at a news conference, Russian Foreign Minister Sergey Lavrov said that the UN decision was a mistake that would harm the international body’s image but not a catastrophe and 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.

“This story hasn’t helped strengthen the UN authority,” Lavrov said, adding that recalling the offer looked “unseemly.”

Iran has been the main regional ally of Syrian President Bashar Assad, supporting his regime with advisers, money and material since the uprising began in 2011. Russia has also backed Assad in the conflict, helping him avert US military intervention by securing a deal for the regime to give up its chemical weapons and reportedly supplying it with military gear.

Lavrov, however, insisted that Russia is not supplying Syria with any weapons that are “banned by international agreements and could destabilize the situation in the region and warned that spurning Iran would deepen divisions in the Islamic world and would have a negative impact on global efforts to fight terrorism.

“The absence of Iran isn’t going to help strengthen the unity of the world’s Muslims,” he said.

At the same time, the foreign minister voiced hope for the success of the talks that would put the government and the opposition at the same table for the first time since the start of the conflict three years ago.

“There is no catastrophe, we will push for a dialogue between the Syrian parties without any preconditions,” he said.

A last-minute UN invitation for Iran to join this week’s Syria peace talks threw the long-awaited Geneva conference into doubt Monday, drawing opposition from players across the board.

An Iranian statement said Iran had accepted the offer without “any preconditions,” referring to the terms of the road map set out for the talks.

Ban said he was “deeply disappointed” by Iran’s statements Monday.

The Syrian National Coalition, which had voted late Saturday to attend after months of rancorous debate, issued an ultimatum, saying that Iran must commit publicly within hours to withdraw its “troops and militias” from Syria and abide by a 2012 road map to establish a transitional government. Otherwise, the group said, the UN should withdraw its invitation for Tehran to take part.

After the secretary general withdrew the invitation, the SNC said it would attend the talks, but the main bloc within the Coalition — the Syrian National Council — issued a late-night statement on Monday saying it was quitting the Coalition in protest over its decision to attend the talks, according to AFP.

The last-minute invitation appeared to take the US and its European allies by surprise.

Senior US officials said Iran has not met the criteria to participate in the conference unless it fully and publicly endorses the aims of the meeting.

Speaking to reporters in a conference call, the officials said public statements from Iran fall “well short” of what is require for Tehran’s participation, adding that they expect the UN to reevaluate and reverse its decision unless Iran changes course.

The officials spoke on condition of anonymity because they were not authorized to discuss the matter using their names.

France, another strong supporter of the opposition coalition, took the same line, with the country’s UN ambassador, Gerard Araud, saying Iran “must accept explicitly” the terms of the road map.

Saudi Arabia, a main backer of the Syrian opposition and a bitter regional rival of Tehran, also said Iran is not qualified to attend the conference but stopped short of threatening to boycott.

The negotiations aim to broker a political resolution to a conflict that has killed more than 130,000 people, displaced millions and put entire towns and neighborhoods under military siege in the worst humanitarian crisis in decades.

Diplomats and political leaders acknowledge that the prospects of achieving such a lofty goal any time soon are slim at best — with the opposition riveted by internal divisions. Infighting between rebels in northern Syria has killed more than 1,000 people in the past month.

Both the government and the opposition have suffered enormous losses, but even now, neither side appears desperate enough to budge from its entrenched position. At this point, just getting the antagonists into the same room to start what is expected to be a long process that could drag on for years would be perceived as a success.

Invitations to the one-day meeting of foreign ministers had been subject to approval by the initiating states, Russia and the United States, but the two countries had been at an impasse over Iran.