U.S. Secretary of State John Kerry says Washington hopes to engage with the new government in Tehran but that any progress must be based on concrete steps.
Kerry said that if Iran intends to be peaceful, "I believe there is a way to get there."
He said it would be "diplomatic malpractice" not to test Iran's willingness to comply with international demands over its suspect nuclear program.
Kerry made his comments in Tokyo after a meeting of the defense and foreign ministers of the United States and Japan.
Kerry expressed hope that engagement with Iran can succeed but said nothing would be taken at face value.
Elsewhere, a senior EU diplomat says Western governments are considering allowing Iran to continue some uranium enrichment as part of a possible deal to resolve the dispute over its controversial nuclear program.
In an interview with the Reuters news agency, Lithuanian Foreign Minister Linas Linkevicius said that if the government in Tehran can prove to UN inspectors that its efforts are for purely peaceful purposes, Iran could be allowed to continue enrichment.
Linkevicius -- whose country holds the rotating EU Presidency -- called the idea "a possibility to explore."
He credited Iran's new "rapprochement" with the West under new President Hassan Rohani with the shift, but cautioned, "It's conditional. It is not a done deal."
The new stance would mean easing a long-standing Western demand that Iran suspend all enrichment, due to concerns Tehran could be developing nuclear weapons.
Iran has long denied the charge.
Based on reporting by Reuters, AP, and AFP