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By Tom Miles and Stephanie Nebehay
GENEVA, Dec 20 (Reuters) - Iran remains a sticking point in plans for a conference to end the conflict in Syria, international mediator Lakhdar Brahimi said on Friday, with the United States still refusing to agree to Iran's presence when talks begin on Jan 22.
"On Iran, we haven't agreed yet. But it is no secret that we in the United Nations welcome the participation of Iran," Brahimi told a news conference in Geneva.
"But our partners in the United States are still not convinced that Iran's participation would be the right thing to do."
Brahimi said he would continue to work with Iranian officials if they were not officially invited. He said they had told U.N. Secretary General Ban Ki-moon it would not be the end of the world if they were not present, and they would continue to work with him on the sidelines.
Russian Deputy Foreign Minister Gennady Gatilov told Interfax news agency the Iranian issue might need to be resolved by discussion at ministerial level.
A senior U.S. official said it was difficult to imagine Iran at the talks, since it had not backed an agreement on the conditions for the peace conference laid down in June 2012.
The official also said there were ways for Iran to take part without attending the ministerial-level opening of the talks, but called on Iran to stop sending troops and military funding to pro-government militias including Lebanese Hezbollah in Syria.
Brahimi said he wanted both Syrian sides to release vulnerable prisoners, such as women and children, and to improve humanitarian access as a show of good faith before the Jan. 22 conference opens in Montreux.
"Why doesn't the government unilaterally free the kids that are in prison? Teenagers, quite a few of them, women - there are quite a few of them, old people that were arrested, they were not fighting, they demonstrated, or have been arrested by mistake."
Syria's government has already formed a delegation for the conference, but has yet to give Brahimi the names. The opposition will not have its list of names before Dec. 27, as Brahimi had hoped, but will have it not long after, he said. (Additional reporting by Alissa de Carbonnel in Moscow; Editing by Andrew Roche)