WASHINGTON – Defense Secretary Leon Panetta's pointed warning that the U.S. will strike back against a cyberattack underscores the Obama administration's growing concern that Iran could be the first country to unleash cyberterrorism on America.

Panetta's unusually strong comments Thursday came as former U.S. government officials and cybersecurity experts said the U.S. believes Iranian-based hackers were responsible for cyberattacks that devastated computer systems of Persian Gulf oil and gas companies.

Unencumbered by diplomatic or economic ties that restrain other nations from direct conflict with the U.S., Iran is an unpredictable foe that national security experts contend is not only capable but willing to use a sophisticated computer-based attack.