An Iraqi scientist has given the Central Intelligence Agency nuclear documents and parts that he had concealed for 12 years, a US intelligence official said on Wednesday.

Mahdi Shukur Ubaydi had hidden them from UN weapons inspectors since 1991.

They were concealed in a barrel buried beneath a rose bush in a garden next to his house, said the official speaking on condition of anonymity.

"This is not a smoking gun," the intelligence official said, noting that it also does not mean that Iraq had a nuclear weapon.

He said the items represented a 'complete set of what would be needed to rebuild a centrifuge uranium enrichment programme'.

"He (Ubaydi) also claimed this concealment was part of a secret high-level plan to reconstitute the nuclear weapons programme once sanctions ended," the official said.

"What's significant is these documents and components were deliberately hidden at the direction of Iraq's senior leadership with the aim of preserving the regime's capacity to resume construction of a centrifuge that at some point could be used to enrich uranium for a nuclear device."

Ubaydi voluntarily came forward with the material and he and his family have been relocated, the official said.