Iran has delivered the strongest indication yet it is prepared to make concessions on nuclear issues to end international isolation and sanctions, with the Supreme Leader announcing he was “not against” a diplomatic outreach to the West.

Ayatollah Ali Khamenei declared that a new policy of openness proposed by Hassan Rouhani, the new reformist president, could bring positive benefits for Iran.

He said he believed in “heroic flexibility” as he endorsed “rational foreign policy”.

Mr Rouhani has approved talks between Mohamad Zarif, the US-educated foreign minister, and William Hague, his British counterpart, in New York. There is also growing speculation that a ground-breaking encounter with US diplomats is on the cards.