In a panel Friday at the World Economic Forum in Davos, Switzerland, Barak said he can hardly imagine a stable world if Iran turned nuclear.
"Imagine a nuclear Iran warning that an attack on Hezbollah was an attack on Iran," Barak said. For Israel, that would "clearly complicate any calculation and any actions," he said.
Barak said Iran already has enough low- and medium-enriched uranium for a small nuclear arsenal, stored in bunkers, making it difficult to take action against the country. He said Iran is engaged in activities that have "no other explanation" than the effort to obtain nuclear weapons.
While most of Iran's nuclear facilities are under International Atomic Energy Agency safeguards, the agency's director-general Yukiya Amano said the agency has credible information Iran has engaged in activities related to the development of a nuclear weapon. He said he is dispatching a mission Saturday to Iran to resolve issues of concern.
Richard Haass, a former U.S. State Department official and president of the Council on Foreign Relations, said a nuclear Iran could compel other nations, such as Egypt or Turkey, to develop their own nuclear arsenals.
If the Middle East is already "interesting," he said, with a nuclear Iran it would become "interesting on steroids."