Icahn, a billionaire investor who is known for taking large stakes in companies and pushing for management change, said in the filing with the U.S. Securities and Exchange Commission that his firm had taken the stake on the belief that Gannett's shares were undervalued and that splitting the company could unlock value.

Icahn reported the stake of roughly 15 million shares as of Aug. 4, one day before Gannett announced that it would spin off its print operations, including USA Today, becoming the latest media company to separate faster-growing TV and digital properties from publishing assets.

Icahn said in the filing that he had not spoken to Gannett prior to Thursday. He added, however, that his firm still intended to speak with the company's management and board of directors about its planned split, corporate governance, capitalization, and capital allocation.

Icahn was not immediately available to comment. A Gannett spokesman said: "We are happy to discuss our plans with Mr. Icahn, as we do with all of our shareholders."

In a separate SEC filing Thursday, Icahn showed that he had already taken a 1.2 percent stake, or about 2.7 million of Gannett's shares, during the second quarter ended June 30. After Icahn's disclosure Thursday, Gannett's shares surged 5.7 percent in after-hours trading.

Icahn also showed that that he increased his stake in e-commerce retailer eBay Inc by 3 million shares in the second quarter, putting his stake at roughly 2.5 percent of the company's shares as of June 30.

The investor also showed that he trimmed his stake in Netflix Inc. by about 480,000 shares to 1.8 million shares, but kept his stake in nutritional supplements company Herbalife Ltd. unchanged. Icahn's firm is the top shareholder in Herbalife with an 18.52 percent stake in the company.