SINGAPORE - Mainboard-listed Noble Group has appointed PricewaterhouseCoopers to review how it values some of its assets, after criticism of some of its accounting practices.

PricewaterhouseCoopers will "conduct an assurance review of Noble's mark-to-market models, valuations, and governance framework," Noble said in a filing with the Singapore Exchange on Tuesday.

Asia's biggest commodity trader also announced the set up of an independent board committee that appointed PwC. The committee consists of four non-executive independent Noble board members - Paul Brough (as chairman), Irene Lee, Richard Margolis, and Christopher Pratt.

On completion of the PwC's review, the committee will report to the board and a summary of the review will be released, Noble said.

Criticism of the Noble's accounting practices has taken a sharp toll on its shares. They are down 40 per cent since Feb. 16 when an anonymous group calling itself Iceberg Research published a first report attacking the way the company values its investments.

The Hong Kong-based group has since been engaged in an escalating war of words with other critics such as US short-seller Muddy Waters and Michael Dee, former Temasek senior managing director.

The criticisms centre on the way Noble values its 13 per cent stake in mining company Yancoal Australia Ltd, and allegations that it is concealing the true nature of its debt.

Noble founder and chairman Richard Elman said in a public letter to shareholders on June 11 that the company is battling against rumors and inaccurate statements and pledged to "right the damage" to its share price.