“It may be that there are ways that could happen,” Mr. Kerry added, but he said the question would have to be decided by Secretary General Ban Ki-moon of the United Nations, “and it has to be determined by Iranian intentions themselves.”

Mr. Kerry made the remarks at a news conference in Jerusalem on Sunday morning, before he flew to Jordan and then Saudi Arabia to confer on his efforts to forge a peace agreement between Israel and the Palestinians and other regional issues. Capping a day of whirlwind travel, Mr. Kerry returned to Israel in the evening.

The debate over what role Iran might play at a peace conference on Syria has been one of the major impediments for convening the meeting. Russia, which has backed the Assad government politically and by sending arms, has insisted for some time that Iran be included in the session. Lakhdar Brahimi, the United Nations special envoy on the Syria crisis, has also favored Iran’s participation, on the ground that Tehran is a major power in the region that has been involved in the Syria conflict.

But France and the United States, which have backed the moderate Syrian opposition, have insisted that Iran should not participate unless it first makes clear that it would accept an outcome in which Mr. Assad hands over power to a transitional body. With the planned Syria conference less than three weeks away, Mr. Kerry appeared to signal that the United States might accept a compromise on the terms of Iran’s role so that the conference could proceed.

But the issue raises broader questions about how to best manage the West’s relations with Tehran. So far, the thaw in relations between the United States and Iran has been mainly limited to the November interim agreement to suspend much of Iran’s nuclear program for six months. Technical talks on how to put that interim agreement into effect are still continuing, and it is unclear whether the agreement will be the basis for a more comprehensive accord to roll back Iran’s nuclear efforts.