KRANJ, Slovenia - U.S. President George W. Bush is calling on Europe to help the United States prevent Iran from developing nuclear weapons, calling the threat an incredible danger to world peace.

Speaking in Slovenia at his final European Union-U.S. summit, Bush said Iran has the choice of facing isolation or having better relations with everyone.

He added that the United States and its European allies should work together to make sure that choice is abundantly clear.

Bush spoke as he and EU leaders were poised to threaten Iran with further economic sanctions unless it verifiably suspends its nuclear enrichment.

Iran denies allegations by Washington and a number of its allies that it is trying to develop nuclear weapons.

However, it refuses to halt enrichment aimed at completing the fuel cycle for its nuclear reactors, an activity allowed under the Nuclear Non-Proliferation Treaty.

Uranium enrichment which can generate both nuclear fuel and, if taken to a much higher level, fissile material for the core of nuclear warheads. Iran insists that it has only civilian uses in mind for its nuclear program.

But Bush said Iran "can't be trusted with enrichment.''

Iran must fully disclose any nuclear work and allow the International Atomic Energy Agency to verify that work, he said.

If Iran ends up with a nuclear weapons, "the free world is going to say why didn't we do something about it at the time? ... Now's the time for there to be strong diplomacy,'' he said.

Iran has already refused to give in despite three earlier sets of UN Security Council sanctions.

On global warming, Bush declared, "I think we can actually get an agreement on global climate change during my presidency.''

But he said no global warming agreement can be effective without China and India.

The United States and many of its allies are at odds over how climate strategy should include developing countries and over mandatory emission reductions, among other sticking points.