Obama UN Iran
US President Barack Obama addresses the 68th United Nations General Assembly at UN headquarters in New York (Reuters)

Barack Obama has reached out to Iran by saying he has instructed US Secretary of State John Kerry to pursue diplomatic ways to resolve Tehran's nuclear issue.

Speaking at the UN General Assembly in New York, the US President said he has given Kerry a mandate to start negotiations over a nuclear weapons agreement with Tehran.

"I firmly believe the diplomatic path must be tested," Obama said.

Obama also welcomed the new moderate path set by his freshly elected counterpart Hasan Rohani.

"We are encouraged that President Rohani received from the Iranian people a mandate to pursue a more moderate course," Obama told the UN.

"[However] conciliatory words will have to be matched by actions that are transparent and verifiable."

In an interview with US television network NBC, Rohani refuted any suggestion that Iran intends to build a nuclear bomb, saying it seeks only peaceful nuclear technology.

Iran had previously claimed that its nuclear programme was for peaceful purposes, but Western governments have long suspected Tehran of trying to develop a nuclear weapon.

Last week Rohani and Obama revealed they have been exchanging letters over the nuclear issue. However, it's still unclear whether the two will meet while at the United Nations.

The leaders of the two countries haven't had face-to-face contact in more than 30 years.

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