White House officials on Tuesday said that Iran had declined President Obama's offer to meet with newly-elected Iranian President Hassan Rouhani on the sidelines of the United Nations General Assembly meeting, telling the U.S. it was “too complicated” to do.

“There will be no meeting,” an administration official said Tuesday afternoon. “It was clear that it was too complicated for them.”

In the days leading up the United Nations meeting in New York, speculation had swirled around the possibility of a meeting between Obama and Rouhani.

The new Iranian president has made a number of overtures to the U.S., calling for “constructive” dialogue in an op-ed last week. Iran watchers say Rouhani hopes to relieve crippling sanctions placed by the international community to slow Iran's nuclear program. Iran insists the program is for peaceful energy purposes, but the U.S. charges Tehran with developing nuclear weapons.

Administration officials said they told the Iranians that Obama was open to the two leaders having an “encounter” on the margins of the U.N. meetings but that invitation was declined.

"The Iranians have an internal dynamic that they have to manage and the relationship with the United States is clearly quite different than the relationship that Iran has with other Western nations," a senior administration official said.

Obama and Rouhani on Tuesday had a historic chance to mark a turning point in the two countries tumultuous relationship, but it's unclear whether there will be any breakthrough.

Earlier Tuesday, Obama addressed the United Nations and said he would respond to Rouhani’s outreach by directing Secretary of State John Kerry to pursue nuclear talks with Tehran.

“We are encouraged that President Rouhani received from the Iranian people a mandate to pursue a more moderate course,” said Obama on Tuesday, acknowledging Rouhani’s efforts to change the tone of U.S.-Iran relations.

But Obama also struck an equally firm message and said the U.S. will not waiver in preventing Iran’s pursuit of nuclear arms.

Obama said Tehran must prove it can be trusted by taking actions to prove their commitment.

“To succeed, conciliatory words will have to be matched by actions that are transparent and verifiable,” he said. “After all, it's the Iranian government's choices that have led to the comprehensive sanctions that are currently in place.”

Rouhani is scheduled to speak to the United Nations late Tuesday afternoon.

After the White House announced there would be no informal meeting with Rouhani, reporters asked Obama at the beginning of a bilateral meeting with Palestinian Authority President Mahmoud Abbas whether he was disappointed.

Obama only smiled and mouthed the words, “thank you.”

Before the United Nations general assembly convened, U.S. officials spurred talk of a potential meeting.

Press secretary Jay Carney said last week that Obama was "willing" to have a meeting but said that Tehran must show it was serious about resuming nuclear talks.

Ben Rhodes, deputy national security adviser, said every move between Obama and Rouhani would be highly orchestrated.

“I don't think anything will happen by happenstance on a relationship this important,” he said Monday when asked if the two presidents would shake hands.

Secretary of State John Kerry is slated to meet with his Iranian counterpart next week for talks. That meeting will mark the highest-level talks between Tehran and Washington since the 1979 Iranian revolution.

This story was published at 3:28 p.m. and has been updated.