The AFP's involvement in the case - which Iluka has not disclosed to the share market - comes after Fairfax Media revealed earlier this month that a secret internal inquiry by the Australian miner had embroiled a leading Sierra Leone presidential candidate, a cabinet minister and high-ranking officials in a bribery scandal.

The revelations place Australia's corporate foreign bribery detection regime under the spotlight, along with questions about how much companies need to tell shareholders about corruption allegations.

The latter topic has become contentious this week after the Commonwealth Bank was accused of failing to notify shareholders in a timely fashion about a longstanding investigation by anti-money laundering agency AUSTRAC. Steel maker Bluescope also disclosed recently that it is the subject of a cartel investigation.

Iluka Resources uncovered the suspected bribe payments after it added one of the world's largest rutile mines to its portfolio via the takeover of the London listed Sierra Rutile Ltd for $375 million in December.

In its takeover of Sierra Rutile, Iluka inherited the London firm's liability for past acts of alleged bribery or corruption. This may expose Iluka to investigation by Australian or UK law enforcement agencies.

This means Australian authorities or their UK counterparts may be able to investigate Iluka for Sierra Rutile's past behaviour.

Former Sierra Rutile Ltd chief executive turned Sierra Leone presidential candidate John Sisay is at the centre of the Iluka bribery probe, with the Australian company confidentially telling anti-corruption investigators at the UK Serious Fraud Office of evidence suggesting Mr Sisay supported alleged improper payments.

Iluka has cancelled three mining licences due to the corruption concerns, which include evidence of a $110,000 payment allegedly funnelled to senior officials at the direction of Mr Sisay.

Mr Sisay, a cousin of current President Ernest Koroma, has strongly denied any impropriety, declaring the revelations in Fairfax Media an effort by foreign forces to derail his presidential campaign.

But in responding to questions posed by Fairfax Media, Mr Sisay has now confirmed that Sierra Rutile spent tens of thousands of dollars on flights for a Sierra Leone cabinet minister, Diana Konomanyi. Iluka discovered more than $50,000 of flight payments and has referred them to anti-corruption authorities.

In a statement, Mr Sisay said that the "flight tickets were bought for medical assistance and were fully disclosed in SRL accounts."

"The Minister of Lands [Ms Konomanyi] is not involved in any mining-related decisions therefore this was not seen to be a conflict of interest in any way."

Mr Sisay has previously said that while he was chief executive of Sierra Rutile he had not authorised "payments of any kind to any Sierra Leone government officials for any reason".

"I categorically deny the allegation that I oversaw the payments of bribes, whether in the form of payment of travel costs or otherwise, in order to secure mining licences," he said in a statement to Fairfax Media earlier this month.

Mr Sisay said Iluka had not raised any issues about any payments by the company.

Nor, he said, had any investigators from Australia, Sierra Leone or "anywhere else" contacted him about the matter.

Iluka has declined to confirm if the federal police are involved in the bribery inquiry and, until Fairfax Media's revelations, had not told the market about the involvement of the British Serious Fraud Office in examining the bribery allegations.

But the AFP confirmed to Fairfax Media that it had "commenced an evaluation into" the bribery allegations.

Iluka has defended its cautious approach to detailing the extent of the alleged bribery scandal to shareholders, stating that the firm's board believes the issue to be financially immaterial.

Corporate corruption and governance expert and partner at Johnson Winter & Slattery, Robert Wyld, said directors of firms facing allegations like those involving Iluka or the CBA faced a difficult decision about how much information they needed to disclose.

He said that while the possible fines arising from a bribery or anti-money laundering prosecution may not materially affect a company's balance sheet, they must consider how any damage to reputation could affect the share price.

Mr Wyld said he generally favoured companies being more forthcoming with disclosure, adding that this was a trend being encouraged by regulators.

"Transparency is generally much better than non transparency but you have to do it in an informed way because what is known to the company at any point in time might be limited," he said.

"The impact of a corruption probe may be blown out of proportion or the probe may be resolved without an adverse finding."

On Friday Iluka's shares lifted to a fresh three-year high at $9.65.