The UN International Atomic Energy Agency has agreed a roadmap with Iran on Tuesday aimed at resolving all outstanding questions about the country's nuclear programme by the end of the year, the IAEA's director general said on Tuesday.

The agency's announcement came hours after diplomats told Reuters that an historic political deal on curbing Iran's nuclear programme in exchange for easing sanctions had been reached.

Allowing the IAEA to issue a final report on the possible military dimensions (PMD) of Iran's past nuclear activities will be a precondition to significant sanctions relief, diplomats say.

"By 15 December 2015, the Director General will provide... the final assessment on the resolution of all past and present outstanding issues," the IAEA's Yukiya Amano said.

For months, Iran had been stalling a UN probe into the possible military aspects of its past nuclear activities, relating mostly to the period before 2003, saying the agency's data for its investigation was fabricated.

Future access to Iran's Parchin military site, which the agency had repeatedly sought, is part of a separate "arrangement", Amano added.

Iran's nuclear chief Ali Akbar Salehi told Iran's ISNA news agency that the country's red lines had been respected with regard to international access to Parchin. -Reuters