Iran is not among the "first round" of nations invited to attend Syria peace talks in Switzerland later this month, a U.N. spokesman said.

Secretary-General Ban Ki-moon began sending out invitations Monday. U.N. spokesman Farhan Haq confirmed that Iran is not among them, but he added, "The secretary-general is in favour of inviting Iran."

Invitations to the talks are subject to approval by the "initiating states," Russia and the United States, Haq said. They approved the list at a Dec. 20 meeting with U.N. officials.

Haq did not name the other invitees, but the U.N. said they included Syrian and other international participants.

The United States and Russia have not yet agreed on Iran's role in the talks, but Haq says the United Nations hopes that can be resolved at a Jan. 13 meeting between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov.

Kerry on Sunday told reporters that Iran could play a constructive role in finding a resolution to Syria's civil war, even if Tehran is not a full participant in the peace talks.

The U.S. has objected to Iran's participation because it hasn't publicly endorsed the principles from an earlier peace conference that called for a transitional government in Syria, and is backing militias, including the Iranian-allied Lebanese Hezbollah group that has aided the troops of Syrian President Bashar Assad.

"If Iran doesn't support that, it's difficult to see how they are going to be a ministerial partner in the process," Kerry said. "Now could they contribute from the sidelines? Are there ways for them, conceivably, to weigh in? ... It may be that there are ways that that could happen," Kerry said.

About two dozen nations plan to send foreign ministers to a daylong gathering Jan. 22 at a Montreux hotel, with Ban presiding. Syria's warring factions have been invited.

The peace talks will start Jan. 24 at the U.N.'s headquarters in Geneva with meetings between Syrian President Bashar Assad's delegation and Syrian opposition groups. The meetings will be moderated by the U.N.-Arab League special envoy to Syria, Lakhdar Brahimi.

Assad's government has said the president will not surrender power and may run again in elections due later this year.

The death toll from Syria's 3-year-old civil war has been estimated at more than 100,000.