Activist investor Carl Icahn said Wednesday he has invested some $3 billion in Apple, and claimed the tech giant is "doing a disservice to shareholders" by not increasing its share buyback.

Icahn's comments made on Twitter suggested tensions rising with the iconic California maker of iPads and iPhones, after having met chief executive Tim Cook for dinner last year to press his case to do more for shareholders.

"Having purchased $500 million more $AAPL shares in the last two weeks, our investment has crossed the $3 billion mark yesterday," Icahn said in a tweet.

Moments later, he said in another tweet that Apple "is doing great disservice to shareholders by not having markedly increased its buyback. In-depth letter to follow soon."

At $3 billion, Icahn's stake remains a modest 0.6 percent of Apple, which has a market value above $500 billion based on its latest share price.

But the corporate raider, who unveiled his investment in Apple last August, is continuing to press for an increased stock buyback which could boost the value of shares.

Last year, Apple agreed to a plan to return some $100 billion to shareholders including $60 billion in buybacks.

Icahn, however, has talked about a bigger share buyback, at one point proposing $150 billion. In December, he said he would make a formal proposal to the tech giant's board of directors but scaled back his idea for a $150 billion program.

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

Apple stock was up 1.47 percent at $557.12 at 1620 GMT.

Taiwan probes Foxconn ex-employees over bribery claims
Taipei (AFP) Jan 22, 2014 - Taiwanese authorities launched island-wide raids to investigate allegations that some former managers at the technology giant Foxconn had solicited bribes from suppliers, prosecutors and the company said Wednesday.

More than a dozen people, including former employees, were questioned and at least one suspect was detained as investigators on Tuesday searched 19 locations including residences and offices of suppliers, local media said citing authorities.

The investigation is the latest setback for the company, which has come under the spotlight after suicides, labour unrest and the use of underage interns at its Chinese plants in recent years.

The "integrity of our employees and suppliers is something we take very seriously... The discovery that a small group of employees and suppliers violated our code of conduct is very disappointing," the company said in a statement Tuesday.

The allegations surfaced after Taiwanese media reported last year that a manager at Foxconn -- which assembles products for Apple, Sony and Nokia -- had been detained by police in the southern Chinese city of Shenzhen.

The Taiwanese manager allegedly solicited and accepted bribes from suppliers in exchange for buying their machines and equipment for the company, reports said, adding that this appeared not to be an isolated case.

Foxconn said at that time it was reviewing its acquisition procedures and the integrity of managers, and that its operations in China had not been affected.

Taiwan's Apple Daily newspaper on Wednesday said a key suspect had allegedly pocketed around Tw$100 million ($3.33 million) in kickbacks from suppliers by using his top position in a procurement committee that buys up to Tw$50 billion of equipment a year.

In its latest statement, the company said the alleged violations were limited to the procurement of consumables and accessory equipment.

Foxconn, also known as Hon Hai in Taiwan, is the world's largest maker of computer components and employs about one million workers at its factories across China.