Noble Group started legal proceedings on Monday at the Hong Kong High Court against its former credit analyst Arnaud Vagner, the person it identified as the mastermind of the Iceberg Research blog.

Noble, Asia's biggest commodity trader by revenue, said in the lawsuit that Mr Vagner and a Seychelles company, Enlighten Ace, conspired to drive Noble's share price down.

The actions by Noble were taken two days after Iceberg released its third report against Noble to raise red flags on the company's governance and debt levels.

In its announcement yesterday, Noble rubbished Iceberg's claims as "inaccurate, unreliable and misleading".

"As a public company we support responsible research. However, Iceberg are not the independent research house they claim to be. Their actions, and their timing, have been calculated primarily to inflict damage rather than to facilitate the distribution of research," Noble said.

The company is suing Mr Vagner and Enlighten Ace for "damages for conspiracy", a writ of summons showed. Mr Vagner must respond to the writ within 14 days.

Yesterday's development was the latest twist in the exchange between Noble and Iceberg since Feb 15, when Iceberg issued its first report on Noble. Since then two more reports have been released to claim that Noble is using accounting loopholes to fabricate asset value and profit in order to hide losses and debts.

Noble has previously provided information about the person behind the reports but did not give a name until yesterday.

Employed by Noble in April 2011, Mr Vagner was a former credit analyst in charge of chartering. His employment was terminated in June 2013 due to "misconduct" and "disruptive behaviour", Noble said.

The Iceberg reports have shook investors' sentiments, and Noble's shares dropped by as much as 30 per cent since mid February to hit a 52-week low at 85 cents last Thursday.

At 1.45pm Singapore time, Noble shares were up 3 cents to 90 cents.