The value of Viacom bonds fell on Wednesday amid growing expectations of a credit rating downgrade after Sumner Redstone, chairman and chief executive, signalled plans for a more aggressive strategy to boost the company's share price.

Viacom, the third largest US media company that owns CBS and the Paramount Pictures film studio, is considering whether it should ?accept a lower rated company? and use money to benefit shareholders, possibly through more share buybacks, Mr Redstone told investors at a conference in Phoenix, Arizona, this week.

On Wednesday, Moody's Investors Service responded by warning it might cut Viacom's A3 credit rating, which affects around $15bn of debt. ?Even if the board decides to refrain from increasing debt leverage at the present time or in the near future, the debt rating could still be downgraded because of concern over management's softened commitment to maintaining the rating,? Moody's said.

As well as contemplating a bigger share buyback programme - Viacom already has an $8bn plan in place - Mr Redstone said several years of underinvestment were now over. ?We were the fastest growing media company in the world and we will be again,? Mr Redstone said. ?A lot of money will be used to increase our presence in the internet.? He also said Viacom was looking to invest in cable networks.

Viacom's shares underperformed last year amid concerns about the performance of its Blockbuster video rental business - since spun off - and its movie studios and radio business. Other media companies have lower ratings than Viacom. By lowering its rating by two notches to, for example, BBB, Mr Redstone said the company would have ?billions? of dollars for share repurchases or acquisitions. Viacom's shares barely moved on Wednesday.

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