US Secretary of State John Kerry on Tuesday suggested that Washington would not insist that Iran answer unresolved questions about its past nuclear activities as part of an investigation by the UN nuclear agency.
US officials have previously said Iran should answer a set of queries the International Atomic Energy Agency has about past Iranian activities and that some sanctions relief under a possible nuclear deal would depend on resolving those questions.
Iran denies the allegations that it may have been seeking to develop a nuclear weapons capability under the guise of a civilian program and that it has carried out nuclear weapons-related research in the past, saying its activities are focused on peaceful applications such as generating electricity.
The IAEA's probe into what it calls possible military dimensions of past Iranian nuclear work is still underway. Tehran says the agency's evidence about past weapons-related activities is fabricated.
Speaking to reporters via teleconference, Kerry suggested Washington was prepared to be flexible on this issue, Reuters reported.
"We're not fixated on Iran specifically accounting for what they did at one point in time or another," Kerry said.
"We know what they did. We have no doubt. We have absolute knowledge with respect to the certain military activities they were engaged in," he claimed.
"What we're concerned about is going forward," Kerry said. "It's critical to us to know that going forward, those (alleged) activities have been stopped, and that we can account for that in a legitimate way."
The United States, Britain, France, Germany, Russia and China have a self-imposed June 30 deadline to finish a long-term deal with Iran which would place constraints on Tehran's nuclear activities for specified durations in exchange for sanctions relief. Officials close to the talks say they will likely run into early July.
An interim deal between Iran and the six powers from April said Iran would need to address the IAEA's concerns under any final agreement.
