An Iranian nuclear scientist who had been reported missing since last summer has defected to the US and is assisting the CIA in its efforts to undermine Iran's nuclear program, ABC News reported Tuesday.

The scientist, Shahram Amiri, has been resettled in the US, according to the report.

The CIA had no comment on the report, a spokesman said.

President Barack Obama said Tuesday he hopes international sanctions against Iran for pursuing its nuclear ambitions will be in place this spring. Iran maintains that its nuclear research is for peaceful purposes and not to develop weapons.

Amiri, who worked at Tehran's Malek Ashtar University, an institution closely connected to Iran's Revolutionary Guard, disappeared last June while in Saudi Arabia on a pilgrimage. While his disappearance led to speculation that he had defected and was assisting the West in its efforts to keep track of Iran's nuclear program, the Iranian foreign minister accused the US of helping to kidnap him.

Citing people briefed on the intelligence operation, ABC News said Amiri's disappearance was part of a long-planned CIA operation to persuade him to defect. The CIA reportedly approached Amiri in Iran through an intermediary who made an offer of resettlement on behalf of the United States, ABC News said.

Amiri has been extensively debriefed since his defection, according to the report, and has helped to confirm US intelligence assessments about the Iranian nuclear program.