Activist investor Carl Icahn lashed out against Apple Inc. gain on Wednesday, saying the iPhone maker was doing shareholders a "great disservice" by refusing to boost its share buyback program.

The billionaire, who has repeatedly urged Apple to return more cash to shareholders, tweeted that he had bought $500 million more shares in the company in just the past two weeks, bringing his total investment to more than $3 billion.

Shares of the world's largest technology company climbed 1.4 percent to $556.71 in morning trading.

Editor’s Note: These 38 Dates Are Key to Bagging $313,038

Known for decades of strong-arm tactics, including proxy fights against major corporations, Icahn has repeatedly made it clear that he does not oppose Apple's management. But neither is he going to walk away from his investment, he told Reuters in November.

"We feel (Apple's) board is doing great disservice to shareholders by not having markedly increased its buyback. In-depth letter to follow soon," Icahn said on Twitter.

"Since tweeting about our large position in $AAPL on Aug 13, when the stock was 468 per share, we've kept buying shares of this ‘no brainer,'" Icahn added on his public profile.

It was unclear how much stock the activist investor, who in August began trying to get Apple CEO Tim Cook to agree to a $150 billion buyback, has recently added to his portfolio. In a letter to Cook made public on October 24, Icahn said he had increased his stake to 4.7 million shares.

In December, Icahn filed a shareholder proposal with Apple for a much smaller additional stock buyback plan of $50 billion, a major step back from previous demands.

Since taking over from the late Steve Jobs, Cook has steered Apple in a more investor-friendly direction, including the establishment of one of the industry's biggest capital return programs.

DEEP POCKETS

But Icahn argues that Apple can afford to share much of its cash pile of more than $146 billion, which in turn would have the effect of taking the stock sharply higher.

Apple is currently in the midst of returning $100 billion to shareholders, including a total share repurchase program of $60 billion. It advised shareholders last month to vote down Icahn's proposal, arguing it had already returned $43 billion in dividends and repurchases over the first six months of that capital return program.

Apple also warned that it needed ready access to cash in a fast-evolving and competitive mobile devices industry.

The company is coming under heavy pressure from Samsung Electronics and Amazon.com Inc. in the smartphone and tablet arena.

Since Icahn first disclosed his slice of the U.S. company in August, Apple's shares have gained 12 percent.

Icahn and Apple did not immediately respond to requests for comment.

Editor’s Note: These 38 Dates Are Key to Bagging $313,038