A long-delayed investigation into whether Iran has sought to develop nuclear weapons could be completed by the end of the year with Tehran’s help.

A long-delayed investigation into whether Iran has sought to develop nuclear weapons could be completed by the end of the year with Tehran's help, the head of the UN atomic watchdog said Saturday.

Following his talks in Tehran earlier this week, UN watchdog chief Yukiya Amano said "progress was made on the way forward, but more work is needed."

"With the cooperation from Iran I think we can issue a report by the end of the year on the clarification of the issues related to possible military dimensions," Amano told reporters before heading into talks with global powers in Vienna.

His comments could mark a breakthrough in one of the thorniest issues still blocking an agreement with Iranian leaders after almost two years of intense negotiations.

Both Iran and the United States have said that the talks are in the endgame, as they inch towards a deal.

The standoff has stalled a probe by the International Atomic Energy Agency (IAEA) into the allegations that before 2003, and possibly since, Iran conducted research work into developing nuclear weapons.

Iran says the accusations are based on bogus intelligence provided to a gullible and partial IAEA by the CIA and Zionist intelligence agency Mossad.

The talks between Iran and the P5+1 -- the United States, Russia, China, Britain, France and Germany -- are aimed at ensuring that all of Iran's pathways to nuclear weapons are cut off. Iran has long denied accusations that it has sought to develop a nuclear bomb.

Amano said the IAEA has stepped up its engagement with the P5+1 in recent months in order to ensure that any deal is "technically sound."

"Once an agreement on the joint comprehensive plan of action, the IAEA is ready to implement the nuclear-related elements when requested," he said.