SINGAPORE - Muddy Waters says it will issue its own "full rebuttal" to Noble Group's categorical rejection on Friday morning of the US short seller's claims that the Singapore-listed company has unsustainable debt levels.

In a Twitter response at 8:51am, Muddy Waters said "MW will be issuing a full rebuttal to the #Noble response. We can already tell it will be fun."

Muddy Waters said on Thursday that Noble "seems to exist solely to borrow and burn cash", and alleged that its 2011 acquisition of Indonesian coal-mining service firm PT Alhasanie was aimed at cutting a quarterly loss that year.

"When we scratched the surface of (the PT Alhasanie) transaction, we found numerous red flags and aggressive actions by Noble," founder Carson Block said.

The report by Muddy Waters follows an attack on Noble's finances and accounts by an anonymous group that calls itself Iceberg Research and by Hong Kong-based GMT Research.

Noble, in a filing with the Singapore Exchange at 8:07am on Friday, rejected the claim that Asia'slargest commodity trader by revenue exists only to borrow and burn cash. While acknowledging that its debt levels fluctuate in between its quarterly reporting deadlines as "more a reflection of market practice," Noble said the changes are "nowhere near" as extreme as Muddy Waters portrayed in its report.

It also rejected what it called Muddy Waters' "unfounded allegations" that it misled investors or manipulated its accounting in the case of the acquisition and disposal of Indonesian mining firm PT Alhasanie. "The acquisition and disposal proceeds of PT ALH and the accounting of them are fully explainable through arms lengths commercial arrangements and third party independent valuations," Noble said.