President George Bush says Iran's nuclear programme remains a threat to peace and the United States will not allow Tehran to develop an atomic weapon.
His administration has pressed the United Nations for more sanctions to convince Iran to halt its nuclear programme which the West suspects is to build weapons.
Tehran denies the accusation. It says the programme is for civilian energy needs.
President-elect Barack Obama has also said that it is unacceptable for Iran to develop a nuclear weapon.
In a speech to the Saban Forum on Friday, President Bush said Iran has been offered diplomatic and economic incentives to suspend uranium enrichment and advised that the West would support a civilian nuclear power programme.
Iran had not accepted these offers and the president said: "Our bottom line (is) clear: For the safety of our people and the peace of the world, America will not allow Iran to develop a nuclear weapon."