Iranian President Hassan Rouhani vowed Wednesday that his country will never develop nuclear weapons, telling NBC News that he is open to diplomatically resolving issues surrounding his country’s controversial nuclear program.

In an interview with NBC’s Ann Curry, Rouhani said that — even with Supreme Leader Ayatollah Ali Khamenei, a looming presence in Iranian society — he has “full power and has complete authority” to make a deal with others on nuclear matters.

Yet Rouhani appeared relatively optimistic Wednesday. He spoke about getting a letter from U.S. President Barack Obama after his recent election and inauguration, saying the U.S. president congratulated him and raised certain issues. Rouhani said he wrote back offering Iran’s viewpoint, describing the tone of the exchange as “positive and constructive.”

If they do and there are “negotiations without threats,” Rouhani added, then “the way for interaction is open.”