During visits to Colombia, Brazil and Chile this past week, Pentagon chief Leon Panetta underscored their importance as military partners in the Pacific, where China is challenging U.S. influence in a number of countries. As those defense relationships grow, officials say it can only help U.S. economic and political ties across South America.

Panetta's talks also focused on how the United States can support their military efforts, including those directed at the expanding threat of cyberattacks, according to several senior defense officials who spoke on condition of anonymity because the meetings were private.