(Reuters) - A former analyst with Moody's Corp has accused the credit ratings agency of issuing inflated ratings, and has taken his concerns to U.S. congressional investigators, the Wall Street Journal reported on Wednesday.

In a letter dated July, obtained by the paper, Eric Kolchinsky accused Moody's Investor Service of issuing a high rating to a complicated debt security in January, in spite of it being aware it was planning to downgrade assets backing the securities.

"Moody's issued an opinion which was known to be wrong," Kolchinsky wrote, along with detailing other instances of inflated ratings issuance, according to the paper.

The paper said a Moody's spokesman declined to comment on the January rating under scrutiny, but had said Kolchinsky refused to cooperate with an investigation into the issues he raised, and was suspended with pay.

Kolchinsky is scheduled to testify on ratings firm reform before the House Committee on Oversight and Government Reform on Thursday, the paper said.

Moody's was not available to comment.

(Reporting by Biswarup Gooptu in Bangalore; Editing by Dan Lalor and Chris Wickham)