The UN chief is "dismayed" over the development after he announced the invitation of Iran to an upcoming conference on Syria scheduled in Switzerland, and is " urgently considering his options", a UN spokesperson said here Monday.

The UN Secretary-General Ban Ki-moon is "dismayed by the development regarding the participation of the Geneva Conference on Syria", which is scheduled Wednesday in Montreux, Switzerland, Martin Nesirky told reporters, noting that "some key participants have conditioned their acceptance to the invitation to the inclusion or exclusion of other delegations."

"Iran, despite assurance provided orally to the secretary- general, has made a disappointing public statement," suggesting it refused to back a June 2012 plan for a political transition in Syria, the spokesperson said.

Ban said "It is time to push for peace in Syria and not the time to add conditions."

"The secretary general is currently urgently considering his options in light of the disappointing reaction of some participants," and the UN is expected to announce further movements regarding the peace talk after Ban considered his options, the spokesman said.

Ban announced Sunday that he had invited Iran to attend the one- day conference, noting that "the expanded international presence on that day will be an important and useful show of solidarity in advance of the hard work that the Syrian government and opposition delegations will begin two days later in Geneva."

After the announcement, US State Department spokeswoman Jen Psaki said that the invitation should be withdrawn unless Tehran publicly states its support for the full implementation of the Geneva I communique signed on June 30, 2012, which agreed to establish a transitional governing body in Syria.

Iranian Deputy Foreign Minister for Arab and African Affairs Hossein Amir-Abdollahian confirm on Monday the invitation, but stressed that his country will not attend the meeting with a precondition.

Syria's main opposition group Syrian National Coalition said on Monday that it suspends the participation unless UN rescinds its invitation to Iran or Iran accepts the Geneva I communique.