The Senate intelligence committee is looking into allegations that the government routinely listened in on phone calls of American military and humanitarian aid workers serving overseas.

ABC News first reported the charges, citing one current and one former military linguist. They are contained in the book "The Shadow Factory," to be published next week.

The linguists say National Security Agency interceptors routinely monitored and recorded the private calls of U.S. military personnel, Red Cross and other humanitarian workers. Personal discussions that had entertainment value, such as pillow talk or phone sex, were shared among intercept operators, according to the linguists.

Intelligence committee chairman Sen. Jay Rockefeller calls the allegations "extremely disturbing."

The NSA says the agency has already investigated some of the allegations and found them to be unsubstantiated.

(Copyright 2008 by The Associated Press. All Rights Reserved.)