The investment firm of William Ackman recently bought 146.5 million shares of Citigroup, the activist investor told CNBC Wednesday without detailing the reason behind the purchase.
At the end of his speech at the 15th annual Ira Sohn investment research conference, Ackman told reporters, "And by the way, we bought about 150 million shares of Citigroup, but I don't have time to talk about it."
Ackman is the managing member of Pershing Square Capital Management.
Shares of Citigroup closed 2.1 percent higher Wednesday.
-- Reuters contributed to this report