Liberia's justice minister on Wednesday announced he would step aside from a probe into a contested oil deal, as he used to be head of the country's national oil company.Frank Musa Dean had been appointed to head the probe just six days earlier by Liberia's newly-elected president, George Weah, who has vowed to crack down on corruption.In a statement, Dean said he had decided to step aside from the probe - initiated by an undercover investigation by the NGO Global Witness - in the interests of transparency."The decision to recuse myself is based on the fact that I served as President and Chief Executive Officer of NOCAL [the National Oil Company of Liberia] between 2004 and January 2006," he said.The controversy stems from a deal in 2013, when the US oil major Exxon Mobil paid $68.5m for a licence to exploit a Liberian oilfield called Block 13.It bought Block 13 from a company called Broadway Consolidated/Peppercoast (BCP), which had initially been awarded the licence from NOCAL in 2005.In a report released on March 29, Global Witness said it had evidence that in 2005 BCP was part-owned at the time by Liberia's minister for mining and a deputy minister - a breach of Liberian law.Corporate documents, it said, show "Exxon knew that Block 13 was originallKEEP UPDATED on the latest news from around the continent by subscribing to our FREE newsletter, Hello Africa.FOLLOW News24 Africa on Twitter and Facebook. y awarded through bribery and that its purchase of the oil block could enrich former officials who might have been behind BCP."Global Witness' report also said "bonuses" of $35 000 were made to senior Liberian officials after Exxon acquired Block 13.President Weah had immediately ordered a probe into the scandal and named Dean as lead investigator. But Global Witness on Monday said his appointment was "a clear conflict of interest.""President Weah has promised Liberians that he will tackle Liberia's endemic corruption. This is his first major test in office to see if he will make good on that promise," said campaigner Jonathan Gant. "Calling for this investigation is a good start. Now the president should ensure it is independent and fair - and it cannot be as long as it is led by Justice Minister Dean."