The announcement by Ban Ki-moon, the United Nations secretary general, that he had invited Iran to a peace conference to end the war in Syria drew strong objections on Sunday from American officials, who suggested that Iran had not met all the conditions for attending and that the invitation might need to be withdrawn.

At the heart of the dispute is whether Iran has accepted the terms of the talks, which begin Wednesday in Montreux, Switzerland: to establish “by mutual consent” a transitional body to govern Syria. Mr. Ban said he had been privately assured that Iranian officials “welcome” those rules and that they had pledged to play “a positive and constructive role.”

American officials said they had been in regular communication with the United Nations over the requirements Iran would need to meet to be invited, but they appeared to have been caught off guard by Mr. Ban’s hastily organized news conference. They pointed out that Iran had not publicly accepted the formal mandate for the conference, which was agreed upon in Geneva in 2012 and is known as the Geneva communiqué.

“If Iran does not fully and publicly accept the Geneva communiqué, the invitation must be rescinded,” Jen Psaki, a State Department spokeswoman, said in a statement.