Iraqi Prime Minister Haider Al Abadi on Saturday directed the country's highest corruption watchdog to investigate claims of graft in the awarding of oil contracts by the Opec exporter and urged the courts to prosecute.

A joint report this week by Australia's Fairfax Media and the Huffington Post, citing hundreds of thousands of emails, linked energy services company Unaoil and several international oil companies to corrupt practices such as claims of bribery in countries including Iraq.

"Al Abadi directs the Integrity Commission to take legal measures and calls on the judiciary to open immediate legal proceedings concerning the grave newspaper reports," according to a statement from his office.

Iraq, which relies on oil exports for most of its revenue, has been plagued by corruption and mismanagement for years, ranking 161 out of 168 on Transparency International's Corruption Perceptions Index in 2015.

Graft continues to eat away at the government's resources as it struggles with high spending due to the costs of the war against jihadist group Islamic State, which seized a third of Iraq's territory in the north and west in 2014.

Abadi has pledged to battle corruption and on Thursday proposed a cabinet reshuffle aimed at weakening patronage networks, but he faces resistance from politicians who fear reform would undermine their wealth and influence.

The report named several Iraqi officials, including then-oil minister Hussein Al Shahristani who it alleged had accepted millions of dollars in bribes to influence the awarding of lucrative contracts.

Shahristani, now outgoing minister of higher education, has denied the accusations. He said on Saturday he was not aware of any attempt to bribe oil ministry officials during his tenure and had never been in contact with anyone from Unaoil.

"I have not met nor communicated with these people by phone or email - directly or through an intermediary - or in any way whatsoever, neither in the period between 2010 and 2012 nor before or after it," he told reporters. "The first time I heard these names was in this report."

Shahristani, a leader in Iraq's ruling National Alliance coalition, urged the government to investigate everyone named in the report, including himself, and called on the Huffington Post to hand over all the documents it referenced.-Reuters

"The law obligates whoever has information (about corruption) to reveal it," he said.-Reuters