US Secretary of State John Kerry has acknowledged for the first time that a final nuclear deal would not require Iran to detail its past activities in order to lift sanctions on the country.
"We're not fixated on Iran specifically accounting for what they did at one point in time or another," he said by video from Boston where he was recuperating from a broken leg, Press TV reported.
"We know what they did," Kerry added. "We have no doubt. We have absolute knowledge with respect to the certain military activities they are engaged in. What we are concerned about is going forward."
Economic sanctions lie at the heart of nuclear negotiations between Iran and the P5+1 group of world powers.
The US and European officials had previously signalled to maintain sanctions as long as the International Atomic Energy Agency (IAEA) would not issue a clean bill of health for Iran's nuclear programme.
Tehran has made it clear that it would not settle for anything short of complete removal of sanctions if a final deal was to be signed.
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Iran is also cooperating with the IAEA and has pledged to clarify everything about what the West calls military dimensions of the country's nuclear activities in the past.
"The possible military dimensions, frankly, gets distorted a little bit in some of the discussion," Kerry said.
Iran says its nuclear activities are purely civilian, aimed at generating electricity. Years of scouring of the country by IAEA inspectors, meanwhile, has not produced any trace of diversion.
IAEA chief Yukio Amana again verified non-diversion of Iran's nuclear programme in the latest report this month, though sticking to the agency's usual political line that it could not provide assurances about possible undeclared material.
Iran and the P5+1 group are currently holding their last stretch of nuclear talks before their self-imposed July 1 deadline to reach a deal.
Kerry, who would head to Vienna next week, said the talks "remain tough".