The United Nations has formally invited Iran to join the long-awaited Syrian peace talks, which are scheduled to open Wednesday in Switzerland.
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. It was on that basis that Foreign Minister Zarif pledged that Iran would play a positive and constructive role in Montreux."
Iran has long rejected the goal set at a 2012 international peace conference, because a transitional authority would likely exclude Syrian President and major Iranian ally Bashar al-Assad.
The main opposition Syrian National Coalition does not want Iran to take part in the talks, and said on Twitter it would withdraw unless Mr. Ban retracts Iran's invitation.
U.S. State Department spokeswoman Jen Psaki said the United States remains "deeply concerned" about Iran's support of Mr. Assad's government, and that Iran must publicly accept the peace conference's goals or be uninvited from the talks.
Russia, another Syrian ally, has called for Iran to be a part of the negotiations.
Mr. Ban also has 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.
The U.N. chief also welcomed the main opposition group's decision to attend.
Syria says the issue of Mr. Assad giving up power is not up for discussion, so few experts expect the talks 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.