UNITED NATIONS (AFP) – The United States offered to set up “an encounter” between President Barack Obama and his new Iranian counterpart during a UN summit but it proved “too complicated” for the Iranians, a U.S. official said Tuesday.

Confirming that Obama would not meet with Iranian President Hassan Rowhani in New York, the official said the Iranians informed the U.S. on Tuesday that they could not arrange it.

“We have said publicly and we also said privately to the Iranians, that we’re open to having discussions on the margins of UNGA — informal discussions not a bilateral meeting. That proved to be too complicated for the Iranians to do at this point,” a senior administration official said.

Obama and Rowhani have exchanged letters since the latter, seen as more moderate than his predecessor Mahmoud Ahmadinejad, came to office in August.

U.S. officials have welcomed initial signs that the new Iranian government may be prepared to open up and make progress on reining in the country’s suspect nuclear program.

But the Americans have also cautioned that Iran must prove it is serious about taking such steps.