British Foreign Secretary William Hague said on Wednesday he believed talks on Iran's nuclear drive set to open in Geneva were a "historic opportunity".

Hague told reporters during a visit to Istanbul that it was too early to say how the negotiations starting later Wednesday between Iran and world powers would go.

But he added: "A deal is on the table that would be in the interest of all nations including countries across the Middle East.

"The differences that remain between the parties are narrow and I believe they can be bridged through political will and commitment," he said.

"It's an historic opportunity to build agreement on how to curb nuclear proliferation in the Middle East and potentially to set up relations with Iran on a different path."

He declined to be drawn on comments Wednesday by Iran's supreme leader Ayatollah Ali Khamenei that the Islamic republic's archfoe Israel was "doomed to collapse", saying it was the "substance of those talks that matters".

"It is the best chance for a long time to make progress on one of the greatest problems in foreign policy and we should all be conscious of that".