The fate of Syria peace talks was in question Monday after the opposition Syrian National Coalition slammed a United Nations decision to invite Iran to the table and said it would not attend.
"The Syrian Coalition announces that they will withdraw their attendance in Geneva 2 unless Ban Ki-moon retracts Iran's invitation," National Coalition spokesman Louay Safi said in a Twitter post.
The group has given the U.N. until 1900 GMT Monday to withdraw the invitation.
As the deadline approached there was a flurry of behind-the-scenes diplomatic activity at United Nations headquarters in New York. The Obama administration is lobbying for the U.N. to disinvite Iran after Tehran on Monday appeared to change its stance on the terms of its participation.
The United Nations has formally invited Iran to join the long-awaited Syrian peace talks, which are scheduled to open Wednesday in Switzerland.
U.N. Secretary-General Ban Ki-moon told reporters Sunday that he believes Iran "needs to be a part of the solution in Syria," and that Foreign Minister Javad Zarif assured him Iran understands the basis of the talks.
"Foreign Minister Zarif and I agreed that the goal of the negotiations is to establish by mutual consent a transitional governing body with full objective powers," he said. "It was on that basis that Foreign Minister Zarif pledged that Iran would play a positive and constructive role in Montreux."
But Iran on Monday disputed that account. It said in a statement that it could not accept a plan for a Syrian political transition, the ISNA news agency reported.
"Setting such a condition to accept the Geneva 1 agreement for attending at the Geneva 2 meeting is rejected and unacceptable,'' ISNA quoted deputy Foreign Minister Hosein Amirabdollahian as saying.
"Iran will attend the talks without any precondition based on an invitation by U.N. Secretary-General Ban Ki-moon,'' the ISNA report said, quoting Amirabdollahian.
Ban said "intensive and urgent discussions are under way" around his invitation to Iran. Ban told the U.N. Security Council Monday that he will have more to say later in the day.
Ban spokesman Martin Nesirky told reporters Monday that Ban "is dismayed'' at the developments. He added that Iran "has made a disappointing public statement.''
"The statement made today in Tehran by the foreign ministry spokesperson fell short by some measure from what the secretary-general expected to hear," he said.
Reuters quoted a senior U.S. State Deoartment official as saying that the offer to Iran is now likely to be withdrawn.
U.S. State Department spokeswoman Jen Psaki said earlier that the United States remains "deeply concerned" about Iran's support of Syrian President Bashar al-Assad's government, and that Iran must publicly accept the peace conference's goals or be uninvited from the talks.
“This is something Iran has never done publicly and something we have long made clear is required,” Psaki said in a statement. “If Iran does not fully and publicly accept the Geneva communique, the invitation must be rescinded.”
Syrian President Bashar al-Assad told the French news agency, AFP, in an interview published Monday that the conference must focus on terrorism, and that his forces are fighting an extremist group, not a popular uprising.
The Syrian government has routinely classified opposition fighters as terrorists throughout the nearly three-year-old crisis.
AFP quoted Assad saying some of the opposition groups set to attend the conference were "created" by intelligence agencies in Qatar, Saudi Arabia, France and the United States. Each of those nations is a member of the so-called Friends of Syria, which has supported the opposition.
Assad also said there is a "significant" chance he will run again for president, and that he will not hesitate to do so if the public supports his candidacy.
Syria has said the issue of Assad giving up power is not up for discussion at the peace talks, so few experts expect the negotiations will reach this goal. But they say they do hope the discussions will result in increased humanitarian access and local cease-fires to make life easier for Syrian civilians.
Ban said Sunday he invited nine other nations that have an interest in the Syrian civil war to join the talks. He says their presence would be an important show of solidarity.
Kerry warned the Syrian president last week that the U.S. is not out of options to pressure his government to comply with the goals set in the first Geneva conference.
"They can bluster," he said. "They can protest. They can put out distortions. The bottom line is we are going to Geneva to implement Geneva 1. And if Assad doesn't do that, he will invoke a greater response in various ways from various people over a period of time."
The Syrian government considers all rebel forces to be terrorists, and has tried to shift the focus of the proposed peace talks from forming a new government to fighting extremism.
Reuters contributed to this report