Washington is in talks with the UN over the surprise invitation of Iran to Syria peace talks and expects the invite to be withdrawn, a US official said Monday.
Iran has "never endorsed the Geneva I communique" which calls for a transitional government in Syria and "we expect the invitation will be rescinded," a senior State Department official said.
Syrian peace talks, due to open on Wednesday in the Swiss lakeside city of Montreux, were in disarray even before they began after the UN invite to Iran sparked a boycott call from the opposition.
And in an exclusive interview with AFP President Bashar al-Assad also ruled out a power-sharing deal with the opposition.
Another senior US official, in Istanbul meeting with the Syrian opposition, confirmed that they had suspended their agreement to join the talks.
But he said the US delegation was still working under the assumption that the talks seeking a political solution to end the almost three-year war in Syria would go ahead as planned.
The Geneva I communique had talked about de-escalating tensions on the ground, he stressed
"Iran's actions are just the opposite. They are escalating problems on the ground," he said, by sending in Iranian military personnel, mobilizing foreign militias to fight for Assad and providing "substantial military material and they have backed the regime economically. They are doing nothing to de-escalate tensions, and particularly sectarian tensions."
"Based on the official invitation, Iran will participate in this conference without any preconditions," Iranian foreign ministry spokeswoman Marzieh Afkham told the official IRNA news agency.
But Washington said its position had not changed.
"Their statements this morning, yet again, fall far short on meeting the bar... so we continue to believe that Iran should not attend, if it has not endorsed the Geneva communique, and obviously the statements overnight did not do that," the first State Department official added.
UN leader Ban Ki-moon said Monday that "urgent" talks on the peace conference were being held after the Syrian opposition threatened to withdraw if Iran takes part.
"Intensive and urgent discussions are underway and I will have more to say about the situation later in the day," Ban told the UN Security Council.
US Secretary of State John Kerry had been in touch with Ban over the weekend and would most likely speak with him again on Monday, the US officials said.