Intel faces a formal investigation by the U.S. Federal Trade Commission after fighting similar antitrust probes in Europe and Asia, the company said on Friday.

AMD has long accused Intel of abusing its dominance of the $280 billion chip market; it filed suit against Intel in 2005. Intel's microprocessors power more than 80 percent of the world's PCs.

Intel said the company already has given the FTC hundreds of thousands of documents in the agency's two-year-old informal probe and will continue to cooperate.

"By proceeding to a subpoena, the Commission will be able to obtain not only information that Intel has already committed to provide but also information from other parties. Consistent with its standard practice Intel will work cooperatively with the FTC staff to comply with the subpoena and continue providing information," Intel said in a statement..

"The company believes its business practices are well within U.S. law. The evidence that this industry is fiercely competitive and working is compelling. For example, prices for microprocessors declined by 42.4 percent from 2000 to end of 2007. When competitors perform and execute the market rewards them. When they falter and under-perform the market responds accordingly," Intel added.

The FTC investigation is a second blow this week for Intel. On Thursday, the Korea Fair Trade Commission in Seoul ruled that Intel had abused its dominant position in the local market and imposed a fine of $25.6 million. Intel said it would almost certainly appeal.

The company also faces other investigations.

The New York state attorney general opened a formal probe of Intel in January to determine whether it broke state antitrust laws by trying to squeeze out AMD. And one year ago, the European Commission in Brussels charged Intel with selling chips below cost and offering customers huge rebates in an illegal attempt to drive AMD out of the market.

Japan's trade commission concluded in 2005 that Intel had violated that country's anti-monopoly act. Intel said it disagreed with the findings but accepted the commission's recommendation, a move that allowed it to avoid a trial.

In a previous FTC investigation of Intel, the two reached a settlement in 1999.

In addition to the various government investigations, AMD's lawsuit accuses Intel of giving computer makers illegal discounts and retaliating against manufacturers who used AMD chips, or stores that gave significant shelf space to computers with AMD chips. On Thursday, the court in Delaware hearing the case postponed a trial until 2010.