(Reuters) -Short seller Hindenburg Research on Thursday took a short position in Icahn Enterprises LP bonds and said the investment firm led by billionaire Carl Icahn has failed to address every issue it had raised.

Hindenburg's latest move comes a day after the company reported a surprise loss and disclosed it was contacted by U.S. prosecutors, though it was not clear if it was related to the short seller's allegations made last week.

The short seller said Icahn's latest disclosures raise critical new questions about margin loans and continued portfolio losses, sending the investment firm's shares down 4% in premarket trading.

"We are short units of Icahn Enterprises and have initiated a short position in IEP bonds," Hindenburg said, adding that failure to disclose basic details about the margin loans represent a "near-term critical threat to IEP unitholders".

The short seller, whose reports on companies have erased a big chunk of their value, had criticized the investment firm for over-reporting its finances and accused it of relying on a "Ponzi-like" structure to pay dividends.

Icahn called the report "self-serving" and vowed to take appropriate steps to "fight back". Known for his face-offs with industry heavyweights such as AIG and McDonald's Corp, the billionaire has never seen his firm become a target of corporate activism.

Icahn owns about 84% of IEP, according to the investment firm's latest quarterly update. He has pledged about 202.6 million of the depositary units he owns for loans as of May 9.

That was much higher than the 181.4 million units Icahn had pledged earlier.

(Reporting by Jaiveer Singh Shekhawat in Bengaluru; Editing by Arun Koyyur)