SINGAPORE (Reuters) - Noble Group has brought forward its first-quarter results announcement by two days, but the Asian commodity trading giant under attack from a research firm over alleged improper accounting did not give a reason for the move.

Mainboard-listed Noble said in filing with the Singapore Exchange on Tuesday morning that it would now report January-March earnings later today after trading hours. It had previously said on its website that the results were due on Thursday, May 7.

Noble is Asia's biggest commodity trader by revenue. Its shares have slumped by as much as a third since Iceberg Research issued the first of three reports in mid-February alleging improper accounting.

Noble has repeatedly rejected Iceberg's claims and has also pledged to improve transparency about its operations. Analysts expect the company to detail its accounting methods in its first-quarter results announcement.

Last month, Noble's shareholders approved the company's 2014 accounts, providing some backing to the embattled company.