US Secretary of State John Kerry has said Washington hopes to engage with the new Iranian administration.
However, he said any advances must be based on concrete steps by Tehran to give up its nuclear weapons programme.
If Iran intends to be peaceful, "I believe there is a way to get there," Mr Kerry told a news conference in Tokyo after a meeting of the two countries' defence and foreign ministers.
Mr Kerry expressed hope that engagement with President Hassan Rouhani's government can succeed but said nothing would be taken at face value.
Discussions would be based on a series of steps that guarantee "we have certainty about what is happening," Mr Kerry said.