Washington on Tuesday said the operation, carried out just days ahead of the 28 June handover of power to the Iraqi interim administration, was aimed at preventing the materials' use for the manufacture of a radiological bomb or in a nuclear weapons programme.
"This operation was a major achievement for the Bush administration's goal to keep potentially dangerous nuclear materials out of the hands of terrorists," Energy Secretary Spencer Abraham said in a statement.
"It also puts this material out of reach for countries that may seek to develop their own nuclear weapons," he said.
The operation involved 20 US nuclear experts from the Energy Department's secret laboratories as well as an undisclosed number of US troops.
US personnel packed the low-enriched uranium and roughly 1000 other highly radioactive devices, loaded them on a military plane and hauled them to the US on 23 June.
Abraham said the operation was consistent with "relevant United Nations Security Council resolutions" and aimed to "ensure the safety and security of the Iraqi people".
The International Atomic Energy Agency and Iraqi officials were briefed in advance about the removal.
The Bush administration has repeatedly accused neighbouring Iran of running a clandestine nuclear weapons programme.
Iran has persistently denied the charge.