Bush said on Saturday in Santiago, Chile, that the world is determined to thwart any plans to develop nuclear weapons.
"I can report that having visited with the other nations
involved in this collaborative effort that the will is strong, that the effort is united, and the message is clear to Mr Kim Jong-il: Get rid of your nuclear weapons programmes," the US leader said in a speech.
Iranian creation of a nuclear bomb would be intolerable, he added.
Nuclear proliferation and the US-led "war on terror" overwhelmed preparations for an annual Asia-Pacific Economic Cooperation (APEC) summit, which was opening on Saturday by the foothills of the Andes in the Chilean capital.
Protests to continue
The 21-member Apec summit, starting a day after violent clashes erupted between police and anti-APEC, anti-Bush protesters, concludes on Sunday with informal discussions in a retreat at Santiago's neoclassical La Moneda palace.
"The development of a nuclear weapon in Iran is intolerable, and a programme is intolerable, otherwise they will be dealt with, starting through the United Nations"
More protests are expected on Saturday evening.
Bush gave a stern warning to Iran about reports that the Islamic republic has accelerated production of uranium material that could be used to make nuclear weapons.
Iran denies the charges and insists its nuclear programme is strictly civilian.
"This is a very serious matter, the world knows it's a serious matter, and we're working together to solve this matter," he said.
Pressure on Iran
In remarks to newspaper editors and publishers, the US leader said: "The development of a nuclear weapon in Iran is intolerable, and a programme is intolerable, otherwise they will be dealt with, starting through the United Nations.
Violent protests accompanied
the APEC summit in Santiago
"The Iranians need to feel the pressure from the world that any nuclear weapons programme will be uniformly condemned. It's essential that they hear that message."
In a rush of meetings with fellow leaders before the summit, Bush also tried to pull the Asia-Pacific alliance together against Pyongyang's nuclear plans.
"The leader of North Korea will hear a common voice," he said.
Bush met with Japanese Prime Minister Junichiro Koizumi, Chinese President Hu Jintao and South Korean President Roh Moo-Hyun and Russian President Vladimir Putin, all partners in six-party talks with Pyongyang.
"What's very important is for the leader of North Korea to understand that the six-party talks will be the framework in which we continue to discuss the mutual goal we all have, which is to rid the Korean Peninsula of nuclear weapons," he said.
Washington hopes to pull Pyongyang back to the negotiations as early as possible - perhaps as early as this year, but more likely in early 2005, according to a senior administration official.
North Korea, which revealed it had a nuclear weapons programme two years ago, boycotted the latest round of talks in September.