US President George W. Bush said Tuesday that he and German Chancellor Angela Merkel had discussed their cooperation in the nuclear dispute with Iran at this mountain resort in northern Japan. "We talked about the need to continue to work together on Iran. Angela Merkel is a constructive force for good," Bush said during a joint public appearance after their talks on the margins of a rich nation summit. World powers are grappling with Iran's response to a package of diplomatic and economic incentives to end uranium enrichment, which can be a set towards nuclear weapons, curbing Tehran's suspect atomic program.