NEW YORK (AP) — Activist investor Carl Icahn says he has purchased $500 million worth of Apple stock in the past couple of weeks to bring his total holdings in the company to more than $3 billion.

Icahn disclosed the purchases on his official Twitter account on Wednesday. He also criticized the iPhone and Mac computer maker's board, saying it's doing a "great disservice" to shareholders by not increasing its stock buyback significantly.

Apple did not immediately respond to a message seeking comment Wednesday morning.

Icahn has been pushing the company's board to spend more of its cash to repurchase shares.

Shares of Cupertino, Calf.-based Apple Inc. are up $7.29 at $556.36 in morning trading.