The United Nations secretary-general has withdrawn his invitation to Iran to join this week's Syria peace talks, saying Monday that he was "deeply disappointed" by Tehran's declaration that it would not join the discussions if forced to accept 2012 Geneva roadmap.

The Syrian National Coalition's political committee welcomed the UN's move in a statement and said it confirmed its own participation in the so-called Geneva 2 conference.

A spokesman for Ban Ki-moon announced the withdrawal less than 24 hours after Ban surprised the U.S. and others by saying he had invited Syria's closest regional ally.

The invitation was withdrawn shortly after Iran's UN ambassador declared the Islamic Republic wouldn't join the Syria talks if required to accept the roadmap sketched during a 2012 Geneva conference on Syria.

A spokesman for Ban, Martin Nesirky, said senior Iranian officials had assured Ban that Iran understood the terms of his invitation, adding that Ban "is dismayed" at the developments.

"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 Communiqué."

The United States said on Monday it was hopeful after the UN withdrew an invitation that all parties could refocus their efforts to end the Syrian civil war.

"We are hopeful that, in the wake of today's announcement, all parties can now return to focus on the task at hand, which is bringing an end to the suffering of the Syrian people and beginning a process toward a long overdue political transition," State Department spokeswoman Jen Psaki said in a statement.

The talks are set to begin Wednesday in the Swiss city of Montreux, with delegations from the United States, Russia and close to 40 other countries attending. Face-to-face negotiations between the Syrian government and its opponents — the first since the three-year civil war began —start Friday in Geneva.

But Ban's announcement Sunday night that Iran was invited to Montreux angered Syria's main Western-backed opposition group, which over the weekend had announced it would join the talks after intense international pressure.

The opposition set a Monday afternoon deadline, saying Iran had to commit publicly by 1900 GMT Monday to the terms set in the 2012 Geneva talks — the formation of a transitional government for Syria that would pave the way for democratic elections —or the UN should withdraw the invitation.

Senior U.S. officials also said Ban's invitation had to be withdrawn unless Iran fully and publicly endorsed those terms.

Invitations to the Montreux meeting 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.

Amid the anger, Ban said Monday morning that he was "urgently considering his options" in light of the "disappointing conduct of some participants" in the peace talks.

"Throughout the Syrian conflict, the Secretary-General has sought to do everything within his power for a political solution, which is the only path forward," the UN statement Monday afternoon said.

Open gallery view The seat of the Iranian representative in the Syria peace conference room in Montreux, Switzerland, January 19, 2014. Credit: AFP