Activist investor Carl Icahn said Tuesday he wants Apple to launch an additional share buyback of $150 billion to help boost the company's struggling stock value.

Icahn said in a tweet he met with Apple chief executive Tim Cook on Monday over dinner to discuss his idea, and that he would continue talks with head of the maker of the iPhone and iPad.

"Had a cordial dinner with Tim last night. We pushed hard for a 150 billion buyback. We decided to continue dialogue in about three weeks," the Twitter message said.

Icahn indicated in August he would press Apple to increase its stock buyback, in which the company purchases its own shares in a bid to boost its value.

Earlier this year, Apple yielded to pressure from the hedge fund Greenlight Capital, agreeing to return some $100 billion to shareholders over the next two years, including $60 billion in share repurchases.

Apple shares, which topped $700 last September and then slumped below $400, traded up 1.6 percent at $484.41.

A recent IDC survey showed Apple's share of the global smartphone market slipped to 13.2 percent in the second quarter, from 16.6 percent a year ago, while Android's share rose to 79.3 percent.

But Apple is expected to get a boost from its new iPhones, which will have wider circulation in countries like Japan and China.

Icahn has a long history of taking positions in companies that give him the leverage to force changes in management or provide dividends to shareholders.

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APPLE INC