GENEVA (AP) — The U.N. secretary-general says the participation of Iran and Saudi Arabia in the proposed Syria peace talks in Geneva remains a stumbling block that has not yet been resolved.

Ban Ki-moon said Monday that he expects both Syrian government and the opposition groups to send delegations to the talks, planned for this summer.

Ban said that some nations remain divided whether to invite Iran and Saudi Arabia, who have been supporting the warring sides in the civil war that has killed tens of thousands of people, and displaced millions.