Carl Icahn Increases Stake in Herbalife

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Billionaire investor Carl Icahn increased his stake in nutritional supplement marketer Herbalife to 16.5 percent from 15.9 percent, according to a SEC filing.

The stock popped about 2 percent in extended-hours trading following the news. (Click here for the latest after-hours quote)

Icahn now owns more than 16.97 million Herbalife shares.

(Read More: Carl Icahn: Why I'm Betting on Herbalife)

Herbalife has been the subject of a battle between Icahn and Pershing Square's Bill Ackman who is short the stock and accuses the company of being a pyramid scheme.

Icahn first revealed a stake in February and called Ackman's short position a "scheme."

(Read More: Bill Ackman Applauds Call for Herbalife Investigation)

Icahn said he was taking the long position to make money, regardless of his personal feelings about Ackman. "I'm not going to lie to you and say if he gets squeezed, I'm going to cry and do penance," he said at the time.