"We remain seriously concerned about the appalling events surrounding the presidential election, and we're deeply troubled by the proliferation risks Iran's nuclear programme poses to the world," Obama said at the end of a summit of G8 nations in Italy.

"We've offered Iran a path towards assuming its rightful place in the world. But with that right comes responsibilities, and we hope Iran will make the choice to fulfill them, and we will take stock of Iran's promise when we see each other this September at the G20 meeting."