US President George W. Bush on Tuesday called on Iran to explain why it had a secretive nuclear weapons program and warned that any such efforts must not be allowed to flourish "for the sake of world peace." "Iran is dangerous," Bush said after a White House meeting with Italian President Giorgio Napolitano. "We believe Iran had a secret military weapons program, and Iran must explain to the world why they had such a program." Napolitano said he and Bush broadly "share the same concerns, and we express a common commitment" on a variety of issues. "We want to discuss, constructively, our positions on all questions in all tracks," he said. "We just want to give our contributions and our ideas on how to face, successfully, all threats, including the very serious threat of nuclear weaponization of Iran." The two leaders' comments came after Iranian President Mahmoud Ahmadinejad said in Teheran, the Iranian capital, that it was "a step forward" that US intelligence agencies had concluded that Teheran stopped developing its nuclear weapons program four years ago. Ahmadinejad told reporters that an "entirely different" situation between the United States and Iran could be created if more steps like the intelligence report followed. "We consider this measure by the US government a positive step. It is a step forward," Ahmadinejad said. "If one or two other steps are taken, the issues we have in front of us will be entirely different and will lose their complexity, and the way will be open for the resolution of basic issues in the region and in dealings between the two sides," he said. Iran has said its nuclear program is peaceful, but until last week, the United States and Western allies had countered that Iran was hiding plans for a bomb. "Iran has an obligation to explain to the IAEA why they hid this program from them," Bush said, referring to the nuclear watchdog International Atomic Energy Agency. "Iran is dangerous, and they'll be even more dangerous if they learn how to enrich uranium," Bush said. "So I look forward to working with the (Italian) president to explain our strategy and to figure out ways we can work together to prevent this from happening for the sake of world peace." Bush's comments amounted to a renewed effort to keep pressure on Iran after the release of last week's National Intelligence Estimate. That report found that Iran had halted its nuclear weapons program four years ago, and administration officials worry it could weaken their ability to build global pressure on Teheran to stop its uranium enrichment program.