* First half net loss of $1.9 bln
* Books $1.3 bln exceptional loss after revaluing assets
* Net debt up $945 mln in first half
* Shares down 95 pct since Feb 2015 (Adds details, chairman quote)
SINGAPORE, Aug 10 (Reuters) - Commodities trader Noble Group reported a second quarter loss of $1.75 billion on Thursday, its biggest in 1-1/2 years which it had flagged last month, as well as a rise of more than $900 million in net debt in the first half.
Once Asia's largest commodities trading house, Noble is slimming down to its core Asian coal-trading business. Last month, it announced the sale of its U.S. gas and power business and began a process to sell its oils liquids unit.
"Conservative liquidity management, scaling back of risk positions and constraints placed on the Group's access to trade finance lines led to disruption costs and prevented the Group from taking advantage of profitable opportunities," the Singapore-listed company said in a statement on Thursday.
It said the group's operating environment remains difficult, especially after the announcement of a net loss for the first three months of 2017. It said further non-cash valuation adjustments may be recorded following its strategic review.
"In terms of strategic alliances in Asia, those discussions are ongoing," Chairman Paul Brough, a restructuring expert who was appointed this year, told analysts on a conference call.
For the first half to June 30, Noble reported a net loss of $1.9 billion which included $1.3 billion of impairments related to the revaluation of some of its long term commodity contracts. Last year it reported a first-half loss of $14 million.
Noble's market value has plunged by about 95 percent to $340 million from $6 billion in February 2015.
That has led to rating agency downgrades, sales of its assets and fund raising to allay investor worries. The stock is down 80 percent this year.
Noble said its net debt increased to $3.8 billion at the end of June from $2.8 billion at the end of last year.
The Hong Kong-headquartered company said it was still in discussions with its lenders. Noble faces the expiry of a $2 billion credit facility in October - a deadline set after agreeing a four-month extension with creditors.
Richard Elman, who stepped down as chairman this year, remains the company's biggest shareholder, with a stake of just over 18 percent.
Other top shareholders include sovereign wealth fund China Investment Corp and Orbis Investment Management, Thomson Reuters data show. (Reporting by Anshuman Daga; editing by Muralikumar Anantharaman and Jason Neely)