U.S. ratings agency Standard & Poor's on Tuesday cut the credit rating of billionaire investor Carl Icahn's Icahn Enterprises to junk status after the portfolio absorbed declining investment values and higher leverage in the last few months.

S&P dropped the long-term issuer credit rating and senior unsecured debt rating of Icahn Enterprises to double-B-plus from triple-B-minus, the agency said in a statement.

Additionally, S&P said it removed all of Icahn Enterprises' ratings from "CreditWatch" with the outlook at "Stable."

There was no immediate response to an email to Icahn's office seeking comment.

The downgrade reflects Icahn Enterprises' elevated loan-to-value ratio, which S&P now expects to remain between 45 percent and 60 percent over the next 12 months, said S&P Global Ratings credit analyst Clayton Montgomery.

"While part of this increase in leverage has come as the portfolio (most notably CVR Energy, Federal Mogul, and the investment segment) has deteriorated in value over the past year, it has also resulted from a substantial decrease in the amount of cash at IEP, which we net against debt in our LTV calculation," Montgomery said.

As of March 31, Icahn Enterprises's LTV ratio was approximately 50 percent, S&P noted. "However, we estimate that after quarter-end through May 13, 2016, IEP's large publicly traded positions declined by approximately $600 million, which would result in an LTV ratio of about 53 percent, holding all else equal."

Shares in Icahn Enterprises were down about 0.49 percent after the ratings news at $52.49.