IBM, the world's second biggest information technology company, on Wednesday became one of 14 companies to be added to the list of stocks that cannot be sold short under an emergency rule by US regulators.

The latest changes came as regulators continued to revise a list first drawn last week. Short sellers, who sell borrowed shares they expect to drop in price in the hope of buying them back for less, are being partly blamed for contributing to market turmoil and regulators around the world have introduced bans.