Iran ? Iranian Oil Minister Kazem Vaziri-Hamaneh stepped down Sunday, plunging the administration of the world’s fourth-largest oil producing operation back into the uncertainty that has shadowed it under the leadership of President Mahmoud Ahmadinejad.

Vaziri-Hamaneh, a veteran Oil Ministry employee, was confirmed to the post by parliament in December 2005 after the Iranian president unsuccessfully nominated three relatively inexperienced candidates, including a former Revolutionary Guards commander.

Vaziri-Hamaneh was appointed special adviser to the president on oil and gas affairs. Iran’s minister of industry also resigned.

No reason was given for the reshuffle, but Vaziri-Hamaneh is believed to have resisted the president’s attempts to consolidate the oil bureaucracy to weed out high-salaried and, in the view of Ahmadinejad’s administration, unnecessary managers.