Rice on Thursday said Iran had a history of "obfuscation and, indeed, lying to the IAEA", referring to the International Atomic Energy Agency.
"There is a history of Iran not answering important questions about what is going on, and there is Iran pursuing nuclear technologies that can lead to nuclear weapons-grade material," she said on a flight to Moscow.
Rice and Robert Gates, the US secretary of defence, are scheduled to meet their counterparts in Moscow on Friday.
|Putin, left, said there was no objective data |
to show Iran wants nuclear weapons [AFP]
Rice said Russia also shared a similar concern about Iran's nuclear programme.
"That concern was seen very clearly in Russia's offer to Iran to enrich and reprocess in a joint venture and to bring back any spent fuel so that the fuel cycle wouldn't be available to Iran," she said.
"I think there is a reason for that, and that is suspicion about Iran's intentions."
US officials have long accused Iran of trying to develop nuclear weapons behind the facade of a civil atomic energy programme, which Russia is helping to develop.
Tehran says the programme is purely for energy, not weapons.
Vladimir Putin, Russia's president, after a meeting earlier this week with Nicolas Sarkozy, the French president, said there was no proof that Iran is trying to build the bomb.
"We have no objective data that Iran is seeking to make atomic weapons," Putin said. "Therefore, we proceed from the assumption that Iran has no such plans."
The UN is scheduled to move on a resolution for new sanctions - which is also opposed by China - in November.
In Moscow, Rice will also discuss US plans for a missile shield in Europe, which includes placing radars in the Czech Republic and interceptors in Poland, despite strong opposition from Russia.
"We have been very clear that we need the Czech and Polish sites. But we are interested in other potential sites as well and... we may be able to find ways to put that together," she said.
"The real central point is that there isn't a threat from the United States to Russia and from Russia to the United States any longer."