A U.S. Securities and Exchange Commission watchdog said on Thursday that he will expand his investigation of the agency's fraud suit against Goldman Sachs Group Inc to look into concerns raised about the timing of the firm's $550 million settlement.

SEC Inspector General David Kotz said that he will look into the circumstances surrounding the timing of the SEC's settlement reached with Goldman on July 16, according to a letter seen by Reuters.

The investment bank and the U.S. investor protection agency announced an agreement earlier this month to settle the SEC's civil fraud suit, which claimed Goldman misrepresented a debt product tied to subprime mortgages.

The SEC's inspector general had already begun investigating the suit in April, after Republicans in Washington suggested political motives may have been behind the timing of the SEC's decision to sue Goldman over the marketing of the product, called Abacus 2007-ACI. The Commission had voted 3-2 to file the suit against Goldman, with the two Republican commissioners dissenting.

Republican Congressman Darrell Issa had asked Kotz to open an initial probe into the timing of the suit in April. The letter on Thursday which agreed to expand the probe to look at the settlement's timing was also addressed to Issa.

Republicans questioned why the SEC case was filed just before the Senate was due to start formally debating a bill to usher in new rules for Wall Street.

The SEC has denied any political motivation for the decision or its timing.

Congress eventually passed the financial regulatory overhaul, which was signed into law by President Barack Obama on Wednesday.

Kotz said he would review documentary evidence, emails among those who were aware of the timing of the SEC settlement and would seek to conduct interviews of all persons with potential knowledge of the facts and circumstances regarding the settlement, according to the letter.

In the April civil fraud suit, the SEC claimed that Goldman did not tell investors that billionaire hedge fund manager John Paulson was betting against the Abacus product and helped to structure it.

As part of the settlement, Goldman did not admit or deny the charges, but agreed to pay $550 million and admitted that it had failed to disclose certain information in its marketing materials.

(Reporting by Rachelle Younglai and Emily Chasan; Editing by Phil Berlowitz)

Barack obama Goldman sachs Settlement