Iraq has again delayed an auction for a dozen oil and gas exploration blocks, because of changes in contract terms, a top official said on Tuesday.

The bidding round had initially been scheduled for January, but the oil ministry delayed the auction to early March, then to April.

"It will be held from May 30-31, due to changes in the terms of the contracts," Abdel Mehdi al-Amidi, the director general of the oil ministry's petroleum contracting and licensing directorate, told AFP, without specifying the nature of the changes.

"The companies have to study the contracts before deciding," he said.

Iraq first announced the sale, the fourth of energy contracts to foreign majors since 2009, in April 2011. A total of 12 exploration blocks are on offer -- seven gas and five oil.

The blocks are located in the provinces of Basra, Najaf, Babil, Muthanna, Diwaniyah and Dhi Qar, south of Baghdad, Nineveh and Diyala to the north and Anbar to the west.

Iraq is looking to dramatically ramp up its energy output, as crude sales account for the vast majority of its government revenues.

The country is looking to raise its production by around 500,000 bpd this year, upping average daily exports to around 2.6 million bpd, according to the oil ministry.

The government says it will be capable of producing 12 million bpd by 2017.