George Bush, the US president, in his address to the UN General Assembly on Tuesday, accused Iran's rulers of squandering their nation's wealth to fund terrorists and nuclear arms research.
But only hours later, Mahmoud Ahmadinejad, the Iranian president, hit back from the same rostrum, accusing Washington and its allies of abusing the 15-nation UN Security Council to deny Iran the right to peaceful nuclear power that Western states had.
In a week of Muslim protests over Pope Benedict's criticism of their faith, Bush insisted the West was not hostile to Islam, contrary to "propaganda and conspiracy theories".
The US president assailed the leaders of Iran and Syria while appealing to their peoples over their heads.
"Your rulers have chosen to deny you liberty and to use your nation's resources to fund terrorism and fuel extremism and pursue nuclear weapons," Bush told Iranians.
"Your rulers have chosen to deny you liberty and to use your nation's resources to fund terrorism and fuel extremism and pursue nuclear weapons"
US president to Iranians
"Iran must abandon its nuclear weapons ambitions," Bush declared after telling reporters he would push for sanctions if Tehran continued to stall on UN demands to suspend uranium enrichment, which the West suspects is aimed at making a bomb.
But he stressed Washington would prefer to resolve the dispute diplomatically, giving the European Union a little more time to seek a formula for launching negotiations.
Ahmadinejad was not in the chamber at the time, but when his turn came, he delivered an uncompromising tirade against US global dominance, singling out the "illegal" invasion of Iraq and "blanket and unwarranted support" for Israel.
Ahmadinejad said Iran's atomic programme was "transparent, peaceful and under the watchful eyes of IAEA inspectors," a reference to the UN nuclear watchdog.
But he gave no indication of any willingness to comply with the UN call to halt uranium enrichment.
Bush said Syria's leaders had made their country "a crossroads for terrorism" and told Syrians: "In your midst, Hamas and Hezbollah are working to destabilise the region, and your government is turning your country into a tool of Iran."
The US president vigorously rebutted critics, including many opposition Democrats at home, who argue his drive for democracy has destabilised the Middle East, from Iraq to the Palestinian territories, empowered Islamists and spread chaos.
"This argument rests on a false assumption: that the Middle East was stable to begin with," Bush argued.
Yet he faced growing skepticism over his policies on Iran and Iraq, with Kofi Annan, the UN secretary general, warning on Monday that Iraq is in grave danger of civil war while France, Russia and China argue against a rush to sanctions.
Jacques Chirac, the French president, said he opposed setting any deadline for sanctions since dialogue should have priority.
France's Chirac opposed
immediate sanctions against Iran
After meeting Bush, he said they fully agreed on a sequence for launching negotiations with Iran, under which major powers would pledge not to seek sanctions for the duration of talks and Iran would suspend enrichment while negotiations lasted.
In contrast to Bush, Chirac told the assembly: "We do not aim to call regimes into question."
Bush and Ahmadinejad slept at adjacent hotels and addressed the annual Assembly session within hours of each other, but their paths did not cross.
The Iranian president, a strict Muslim, declined to attend a lunch for world leaders, including Bush, hosted by Annan. Other Muslim leaders attended.