SINGAPORE - Noble Group reported net loss of US$1.67 billion (S$2.34 billion) for 2015, as the commodity firm wrapped up a tumultuous year.

The loss, which was a far cry from the US$132 million net profit it reported in 2014, included some US$1.2 billion in exceptional non-cash losses highlighted earlier this week.

It was made to account for the impact of weaker coal prices on asset values.

Excluding the exceptional losses, Noble's adjusted net profit was US$244 million, down 58 per cent from 2014's adjusted profit of US$586 million.

The company's net debt stood at US$3.97 billion as at Dec 31. When including the US$750 million received from the sale of Noble Agri shares, net debt was US$3.22 billion, with a net debt to capitalisation ratio of 49 per cent.

Noble also has a liquidity headroom of US$2.2 billion, with another US$1.7 billion contributed from readily marketable inventory. The total sum of liquidity, at US$3.9 billion, is more than the US$2.5 billion in debt maturing in the next 12 months.

Chief executive Yusuf Alireza stressed that there are bright spots in the Noble's performance, with the underlying businesses still generating earnings.

"Our four energy businesses have generated combined record operating earnings at US$1.3 billion in 2015.

"Now that the disposal of our remaining interest in Noble Agri has become wholly unconditional… We can look forward to generating the returns that we know the 'New Noble' is fully capable of."

The energy business, including oil liquids and energy coal, delivered US$646 million in profit before tax in 2015, up 21.4 per cent year-on-year.

And while the gas and power business saw a 29.8 per cent year-on-year drop in 2015 profit to US$214 million, the performance in the United States market was strong, Noble added.

But the mining and metals segment continued to struggle, reporting a loss of US$229 million in 2015, down from 2014's US$282 million in profit.

These figures indicated the very challenging energy and commodity market conditions that Noble had to navigate in 2015, while battling against allegations of accounting and governance issues from critics such as the Iceberg Research blog.

Just an hour before the results announcement, Iceberg released its fourth full report, saying that Noble's senior management has lost its credibility.

Noble shares closed down half a cent or 1.47 per cent at 33.5 cents.