"The G20 will take a bigger role in economic cooperation than the G8 has in the past," Brown told reporters ahead of this week's meeting of G20 leaders in Pittsburgh.

Brown noted there were $7 trillion worth of foreign exchange reserves which he said were "not necessarily being used in a constructive way."

Brown said he wanted to see the International Monetary Fund come up with an insurance scheme that would lessen some countries' need to accumulate reserves so that they could use those funds to support their economies.

"We are coming to a moment of truth with Iran," Brown said. "We will be proposing fuller and tougher sanctions."