Junk bonds have tumbled to levels not seen in more than six years and billionaire investor Carl Icahn says there’s more to come.

“The meltdown in High Yield is just beginning," Icahn wrote on his verified Twitter account Friday.

Icahn’s comments come as junk-bond investors, already stung by the worst losses since 2008, are the most nervous they’ve been in three years after Third Avenue Management took the rare step of freezing withdrawals from a $788 million credit mutual fund.

The risk premium on the Markit CDX North American High Yield Index, a credit-default swaps benchmark tied to the debt of 100 speculative-grade companies, rose 36 basis points to 514.52 basis points, the highest since December 2012. BlackRock’s iShares iBoxx High Yield Corporate Bond ETF, the largest fund of its kind, fell to the lowest levels since 2009.

The move by Third Avenue, announced on Dec. 9, is the latest omen of stress in a market already beaten down by a prolonged slump in oil prices that has battered the energy sector. The news came as appetite for risk globally is souring as the countdown to the Federal Reserve’s probable interest-rate increase sparked a selloff in equities and other risk assets.

"The timing could not be worse," said Peter Tchir, head of macro strategy with Brean Capital LLC in New York. "Everyone is already nervous about liquidity, oil, the Fed hike -- and you get this extreme event on top of it all. There is a lot of confusion. It’s put people on edge."

Oil declined to the lowest level since 2008, exacerbating losses in high-yield energy debt, which makes up 12 percent of the broader market.

‘Heavy’ Sentiment

Market woes have seen outflows from U.S. high-yield bond funds running at the fastest pace in more than a year as U.S. junk debt has declined 3.6 percent, the first annual loss since 2008, according to Bank of America Merrill Lynch Indexes.

"Sentiment is heavy," said Jerome Conner, who helps oversee about $52.9 billion as portfolio manager and senior investment analyst at Federated Investors Inc. Falling oil prices continue to weigh on markets, and "people see the Third Avenue headline and that contributes to the negative sentiment in the market," he said.