Just because the Iranians were not invited to the conference, Mr. Kerry said, “doesn’t mean that we are opposed to the idea of communicating to find out if they will come on board or under what circumstances or whether there is the possibility of a change.”

Image President François Hollande of France greeted President Fuad Masum of Iraq at the Elysée Palace in Paris on Monday. Credit... John Schults/Reuters

In Tehran, the tone was quite different. Iranian officials gave out flurries of statements to local reporters on Monday, saying that they had rejected multiple invitations by the United States to join the coalition.

On Monday, Ayatollah Ali Khamenei, the country’s supreme leader, issued a scathing and, at times, sarcastic statement on the day he left the hospital after prostate surgery. In remarks posted on his personal website, he said he had enjoyed his recent time in the hospital because he had “a hobby,” which was “listening to Americans making statements on combating ISIS — it was really amusing.” Such statements, he added, are “absurd, hollow and biased.”

The Obama administration has long sought to separate the nuclear talks with Iran from discussions of regional issues, out of concern that Tehran might seek concessions in the nuclear negotiations in return for cooperating on Syria or Iran.

Mr. Kerry also acknowledged that the administration’s previous effort, led by the deputy secretary of state, William J. Burns, to draw Iran into quiet talks on Iraq and other regional issues had not been productive. “The confidential discussions never got to that sort of substance,” Mr. Kerry told reporters.