The United Nations has started inviting participants to this month's Syrian peace talks in Geneva, but has not yet decided whether to invite Iran.
A U.N. spokesman Monday said that Secretary-General Ban Ki-moon is in favor of Iranian participation.
But it is up to the talks' organizers -- the United States and Russia -- to decide who will be there.
Moscow wants Iran to attend while Washington is imposing conditions.
State Department spokeswoman Marie Harf says Iran must support a transitional government in Syria -- which likely would exclude Bashar al-Assad. Harf also says Iran should urge the Syrian government to stop attacking civilians.
Secretary of State John Kerry said Sunday that Iran still could take part in Geneva from the "sidelines." Iran says it will not accept any proposal that does not respect its dignity.