President Obama and Iranian President Hassan Rouhani won't have a historic meeting, or any other informal encounter, during the annual United Nations session after all, two senior administration officials said today.

The sources, who spoke only on condition of anonymity, said that a meeting proved "too complicated for Iranians to do at this point." They did not explain what the complications were.

The White House had signaled for days that an informal meeting, even a handshake, between the leaders was possible. Aides today confirmed that the administration proposed such a "discussion on the margins" to the Iranians but were rebuffed.

"There will be no meeting," one official said. "It was clear that it was too complicated for them."

The officials reiterated that a formal bilateral meeting or negotiation between Obama and Rouhani was never on the table.

Still, the Obama administration signaled today that it wants to move forward with a new round of diplomacy with Iran, affirming a meeting Thursday in New York between Secretary of State John Kerry and Iranian Foreign Minister Javad Zafir.

"That is where this [nuclear issue] would be resolved," said one official. "We would never have a negotiation at this point at the presidential level on the substance of any nuclear agreement. The negotiation is going to take place at the foreign minister level and it's going to take place through the P5-plus-1 process. And that's going to go forward later this week."

The men will attend a previously scheduled meeting of the P5+1, which is seeking to negotiate a resolution of Iran's contested nuclear program. It will mark the highest-level encounter between U.S. and Iranian leaders on the nuclear issue in three decades.

Earlier today, Rouhani was a no-show at a U.N. luncheon for world leaders when he would have shared the room with Obama. Iranian state media said Rouhani skipped the event because alcohol was being served. He later met one-on-one with French President Francois Hollande.

Sasha Mordovets/Getty Images | Richard Drew/AP Photo

Despite the high expectations of a meeting, there were signs from Iran as the day got underway that a presidential meeting might not materialize.

"The assumption that a meeting (between Iranian and American officials) per se could be decisive or help solve problems is absolutely wrong," said Iranian Foreign Ministry spokesperson Marzieh Afkham at a press conference.

"We think that we should wait until a proper time for such a meeting comes," she said. "Our assessment is that the proper time hasn't yet come."