Iran's new president Hassan Rouhani has told an American television audience he is hopeful of a diplomatic breakthrough over Tehran's nuclear weapons programme, insisting his country had no intention of developing weapons of mass destruction.

Speaking before a crucial visit to the United Nations in New York, Rouhani claimed his government had "full power and authority" from Iran's supreme leader to negotiate over the nuclear programme, which the US fears is close to creating a bomb.

"The problem won't be from our side," said Rouhani in his first interview with western journalists since coming to power. "We have sufficient political latitude to solve this problem."

"Under no circumstances would we seek any weapons of mass destruction, including nuclear weapons, nor will we ever," he added in initial clips of the interview with NBC aired on Wednesday night

"We have never pursued or sought a nuclear bomb and we are not going to do so. We are solely seeking peaceful nuclear technology."

Though Iran has long insisted it has only peaceful intentions for its nuclear programme, the reassurances of Rouhani on US television before his trip to New York will help foster hopes in the administration that more moderate political forces are prevailing in Tehran.

President Obama and Rouhani recently exchanged letters following Iranian elections and the two may meet on the sidelines of the UN general assembly next week.

Rouhani even appeared to pay tribute to Obama's handling of the Syria crisis, saying it was not a sign of weakness to seek diplomatic rather than military solutions in such cases.

"We consider war a weakness and any government that decides on peace we look on with respect," the Iranian president said.

He declined to comment on Iran's role in the deal over Syrian chemical weapons recently brokered by Moscow, but added: "We are one of the countries in the region that seeks peace and stability and the elimination of weapons of mass destruction."

Earlier, White House spokesman Jay Carney said Obama welcomed the recent positive noises from Tehran.

"I think it's fair to say that the president believes there is an opportunity for diplomacy when it comes to the issues that have presented challenges to the United States and our allies with regards to Iran," he said. "And we hope that the Iranian government takes advantage of this opportunity."

But Carney said the US will test Rouhani's assertions that he wants to improve relations with the international community.

In his letter, Obama indicated that the US was ready to resolve the nuclear issue in a way that would allow Iran to demonstrate that its program was exclusively for peaceful purposes, Carney said.

Rouhani said of the note he got from the White House congratulating him on his June election: "From my point of view, the tone of was positive and constructive."

"It could be subtle and tiny steps for a very important future. I believe the leaders in all countries could think in their national interest and they should not be under the influence of pressure groups. I hope to witness such an atmosphere in the future."