Shares of Israeli drugmaker Teva slipped briefly in pre-U.S. market trading Monday, after investor Warren Buffett told the cable TV network CNBC he wasn't sure why staff at his Berkshire Hathaway Corp. had bought 18.6 million shares of the company. The stock quickly returned to the level it has traded at since Buffett's company disclosed the Teva investment Feb. 15.

Teva employs more than 1,000 at its North American headquarters in North Wales, Pa., and other suburban Philadelphia locations.

Buffett's company bought the shares and became a nearly 2 percent owner of Teva earlier this month after cutting his stake in General Electric Corp. and expressing disgust at GE's insurance write-offs.

Teva shares rose on that news Feb. 15, as commentators speculated that maybe Buffett saw hidden value in the stock. Teva has lately hovered around $20 a share, after tumbling from more than $30 last Spring to as little as $11 in November on disappointing sales and profits.

Berkshire Hathaway owns almost 2 percent of Teva, according to SEC data collected by Bloomberg LP. The company's largest shareholders is the management group that buys stocks for the Los Angeles-based American mutual funds, which owns around 12 percent. Wellington Management Co., whose clients include Malvern-based Vanguard Group, owns around 4 percent.