Activist investor Carl Icahn has sent a letter to Apple CEO Tim Cook three weeks after demanding the iPhone maker take steps to boost its stock price.

Icahn says in a post on his Twitter account that he sent the letter to Cook Wednesday afternoon. Icahn says he will share the letter Thursday on a new website called "Shareholders' Square Table."

The missive follows up on a Sept. 30 dinner with Cook that Icahn hosted at his New York apartment. During that get-together, Icahn said he lobbied Cook to spend $150 billion buying back Apple Inc.'s own stock. That's more than double the amount that the Cupertino, Calif., company has committed to spend.

Icahn has said his fund has invested about $2 billion in Apple.