One year ago Iranian President Hassan Rouhani, shown here during an interview with state television in Sept. 2013, and President Barack Obama came close to ending the decades-long freeze on face-to-face meetings between the countries’ leaders. (Rouzbeh Jadidoleslam/AP)

A year ago, a historic phone conversation between President Obama and Iranian President Hassan Rouhani, on the last day of the annual U.N. General Assembly, electrified the foreign policy and diplomatic universe.

Rouhani publicly committed to improving relations with the United States, and Obama said he and his Iranian counterpart had agreed to direct negotiating teams to seek a deal on Iran’s nuclear program.

One year later, the two nations have not closed a nuclear deal. Meanwhile, the rise of the Islamic State — opposed by both the United States and Iran — has raised awkward questions about how two countries estranged for 35 years might unite against a common foe.

This year’s General Assembly, which opens this week, presents yet another opportunity for the United States and Iran to test each other’s willingness to engage on a host of issues. Obama and Rouhani will circle each other once again with no plans to meet — a metaphor, perhaps, for the eddy and stall of what seemed a year ago to be bright prospects for change.

Talks on Iran’s nuclear program have been at an impasse for months over what American and other Western officials call Iranian intransigence. Secretary of State John F. Kerry emerged from talks Sunday with Iranian Foreign Minister Mohammad Javad Zarif to say that the United States will keep working on the deal to roll back Iran’s nuclear program in exchange for the lifting of international sanctions on Tehran.

The White House rejects an Iranian suggestion of new concessions made to its nuclear program in exchange for cooperation in the fight against Islamic State. (Reuters)

But Iran has expressed its own frustrations with the American approach to the talks. The United States is “obsessed” with sanctions, Zarif told an audience at the Council on Foreign Relations last week.

“Sanctions have become an end in themselves,” he said. “Sanctions do not serve any purpose.”

The spread of the Islamic State in Iraq and Syria, which might otherwise be an opportunity for cooperation between the United States and Iran, has instead made both nations nervous about how to maneuver around one another. The United States ensured that Iran was excluded from an international conference on strategies to counter the militants last week. Iranian diplomats have said that the United States and other nations are only cleaning up a mess of their own making in Iraq.

Kerry invited Iran to play a constructive role when he convened a U.N. Security Council meeting on the militants last week, but he avoided asking for any specific commitment to work side by side.

Some reports, including one by the Reuters news agency over the weekend, have indicated that the Iranian government is interested in working with the United States against the Islamic State in exchange for flexibility on its nuclear program. The Obama administration said Monday that it would not entertain any effort by Iran to link the two issues.

“The United States will not be in the position of trading aspects of Iran’s nuclear program to secure commitments to take on ISIL,” White House press secretary Josh Earnest said, using an acronym for the militant group.

The nuclear negotiations, which involve six world powers and Iran, are “entirely separate” from the new challenge, Earnest said. The United States will not coordinate military action or share intelligence on the militants with Iran, he added.

Kerry and Zarif are expected to meet again this week, even if Obama and Rouhani do not. On the agenda could be any number of issues that have complicated U.S.-Iranian relations lately, including the arrest of Washington Post reporter Jason Rezaian. The troubled nuclear talks are likely to dominate the discussions.

A senior State Department official, who spoke on the condition of anonymity to describe the private meeting Sunday, did not sound optimistic about the nuclear talks.

“They discussed both the progress that has been made and the work that still needs to be done,” the official said. “Secretary Kerry noted that this week is an opportunity to make additional progress and stressed that it is our intention to do so.”

Last week, another State Department official was more direct.

“The status quo is not doable for any of us. It is not doable for either side,” said the official, who spoke on the condition of anonymity because she was not authorized to discuss the status of the negotiations on the record.

The goal of the talks, from the Western perspective, is to greatly roll back the scope of a program seen as a potential cover for the development of nuclear weapons. Iran would be left with a small uranium-enrichment capability that would allow the government to say that it did not give up what it calls a right to the same scientific technology other nations employ.

Iran has insisted on keeping about three times as many uranium-enriching centrifuges as U.S. and other negotiators propose, according to people familiar with the talks. Diplomats said the best outcome at this point may be a second extension of the deadline for a deal, which was supposed to be concluded by July, or a much smaller and temporary agreement than the comprehensive settlement envisioned a year ago.

“There is mutual lack of confidence on both sides,” Zarif said at the Council on Foreign Relations event.

“The Iranian people and the Iranian government representing them is totally distrustful of the intentions of the United States, to be absolutely honest with you,” he continued. “I won’t be surprised if you tell me that you don’t trust our intentions. So, fine. We’re even.”