Standard & Poor's president Deven Sharma is stepping down, its parent company announced, just weeks after the credit rating agency cut the US' top AAA rating and sent global markets into turmoil.

Sharma, who will take another role in the company before leaving altogether at the end of the year, will be replaced by Citibank's current chief operating officer Douglas Peterson, corporate parent McGraw-Hill said in a statement late Monday.

The US Justice Department is currently investigating the company for its practices regarding mortgage securities that helped trigger the 2008 global financial crisis.

Sharma, 55, "will take on a special assignment working on the company's strategic portfolio review until the end of the year when he will leave the company to pursue other opportunities," the statement read, adding that Peterson, 53, will become the S&P president starting September 12.

Harold McGraw III, chairman, president and CEO of The McGraw-Hill Companies, described Peterson as "a seasoned executive with more than 25 years of global experience in financial services, risk management and capital markets."

Peterson's resume includes his role as the CEO of Citigroup Japan from 2004 to 2010, the statement read.

McGraw thanked Sharma "for his dedicated leadership of S&P."

US officials lashed out at S&P after it docked the country's credit rating from AAA to AA+, accusing the agency of committing a $2 trillion math error and of using a faulty baseline. S&P has stood by its analysis.

S&P said the August 5 decision to downgrade the US long-term credit rating came as a result of divided US lawmakers failing to agree on a deal to reduce the ballooning US public debt by some $4 trillion over 10 years.

The decision followed a bruising fight on Capitol Hill over raising the country's congressionally-set debt ceiling, which resulted in a limited agreement to cut some $2 trillion over that period.

The Justice Department probe, launched before the credit downgrade, is looking at whether S&P analysts wanted to lower the ratings of certain bonds backed by mortgage debt but were prevented from doing so by superiors due to business concerns.

Under Deven, Standard & Poor's was split into two separate organizations, the S&P credit ratings service and McGraw-Hill Financial. Deven "assisted us with the creation of these two high-growth segments and was then ready for new challenges," the statement read.

The New York-based McGraw-Hill Companies, perhaps best known in the United States as a school and college textbook publishing company, is also the parent company of Platts, a specialty publication and news service focusing on minerals and energy, the market research company J.D. Power and Associates, and several publications including Aviation Week.

Meanwhile, two activist investors at McGraw-Hill that together own 5.2 percent of the company hope to break the media conglomerate into four parts, US media reported.

The investors -- Hedge fund Jana Partners LLC and the Ontario Teachers' Pension Plan -- said in a presentation to the company on Monday that "the recent regulatory and political scrutiny around the S&P Ratings business highlights the drawbacks of housing wholly unrelated businesses together," the Wall Street Journal reported.

The public scrutiny around S&P "serves as an overhang on McGraw-Hill's valuation," the investors said, according to the Journal

The Fitch credit ratings agency downgraded The McGraw-Hill Companies to 'A' from 'A+' and put the company on a negative ratings on August 19.

The move was in part based on advance notice of the plan of the activist investors, and in part because McGraw-Hill itself publicly announced "significant actions" in the second half of 2011, likely related to spinning off some of its operations.

"Fitch believes that leverage may increase as a result," it said in a statement.