US President George W Bush has warned of the dangers he says are posed by Iran, in a speech in its Gulf neighbour, the United Arab Emirates.
Mr Bush said Iran threatened the security of all nations and should be confronted "before it's too late".
In a speech in Abu Dhabi on the latest leg of a Middle Eastern tour, he also urged the region to embrace democracy.
Meanwhile the UN's atomic watchdog said Iran had agreed to clear up questions about its past nuclear activities.
The statement by the IAEA said Tehran would provide details in the next four weeks.
Mr Bush's address in Abu Dhabi was described by his aides as the keynote speech of his regional tour.
He told delegates at the Emirates Centre for Strategic Studies and Research (ECSSR) that more open societies would foster the Middle East's immense "human capital".
He said there had been advances in the region, but also setbacks.
Without fair elections and freedom of speech, "you cannot expect people to believe in the promise of a better future", he added.
Mr Bush said spreading freedom and democracy was the best way to defeat radicalism.
President Bush arrived in the UAE amid a light drizzle
America and its democratic allies would prevail over extremists like al-Qaeda, he said, because they have "freedom and justice written into our hearts by Almighty God... no terrorists can take that away".
The BBC's Matthew Price, travelling with Mr Bush, says the president has sounded more nuanced on this trip than previously, and has spent much of it making suggestions rather than demands.
But that may not be how it plays to the "streets" of the Middle East.
Many people will see US foreign policy as militaristic, following its invasions of Iraq and Afghanistan, and will view Mr Bush's words on Iran as a call to arms - even though they were not, our correspondent says.
In fact, in his speech he sought to reach out to the people of Iran, saying: "You're rich in culture and talent. You have the right to live under a government that listens to your wishes, respects your talents and allows you to build better lives for your families."
However, he repeated his allegation that Iran was "the world's leading state sponsor of terror", funnelling arms and funds to militant groups like Hezbollah and Hamas, the Taleban and Shia fighters in Iraq.
He said Iran had defied the United Nations and destabilised the region by failing to be transparent about its nuclear programme.
Earlier on Sunday, during a visit to Bahrain, President Bush met some of the sailors whose ships the US says were confronted by Iranian speedboats last weekend.
Mr Bush also addressed the Middle East peace process, trying to encourage support from his Gulf Arab allies.
In particular, he is attempting to persuade them to back Palestinian Authority President Mahmoud Abbas as he negotiates with the Israelis.
While visiting Israel and the Palestinian Territories on Thursday, he said Israel must end its occupation of some Arab land to enable the creation of a viable Palestinian state.