WASHINGTON – U.S. authorities believe that Iranian-based hackers were responsible for cyberattacks that devastated Persian Gulf oil and gas companies, a former U.S. government official said. Just hours later, Defense Secretary Leon Panetta said the cyberthreat from Iran has grown, and he declared that the Pentagon is prepared to take action if America is threatened by a computer-based assault.

The former official, who is familiar with the investigation, said U.S. authorities believe the cyberattacks were likely supported by the Tehran government and came in retaliation for the latest round of American sanctions against Iran.

Before Panetta’s remarks on Thursday, U.S. officials had said nothing publicly about the Gulf attacks or the investigation. But Panetta described them in a speech to business leaders in New York City, saying they were probably the most destructive cyberassault the private sector has seen to date.

Panetta did not directly link Iran to the Gulf attacks, but he said Tehran has “undertaken a concerted effort to use cyberspace to its advantage.” And, he said the Pentagon has poured billions into beefing up its ability to identify the origin of a cyberattacks, block them and respond when needed.

“Potential aggressors should be aware that the United States has the capacity to locate them and hold them accountable for actions that harm America or its interests,” said Panetta in a speech to the Business Executives for National Security.

A U.S. official acknowledged that the Obama administration knows who launched the cyberattacks against the Gulf companies and that it was a state actor.

U.S. agencies have been assisting in the Gulf investigation and concluded that the level of resources needed to conduct the attack showed there was some degree of involvement by a nation state, the former official said. The officials spoke on condition of anonymity because the investigation is classified as secret.

While Panetta chose his words carefully, one cybersecurity expert said the Pentagon chief’s message to Iran in the speech was evident.

“It’s not something where people are throwing down the gauntlet, but I think Panetta comes pretty close to sending a clear warning (to Iran): We know who it was, maybe you want to think twice before you do it again,” said cybersecurity expert James Lewis of the Center for Strategic and International Studies. “I think the Iranians will put two and two together and realize he’s sending them a message.”

The cyberattacks hit the Saudi Arabian state oil company Aramco and Qatari natural gas producer RasGas using a virus, known as Shamoon, which can spread through networked computers and ultimately wipes out files by overwriting them.

Senior defense officials said the information was declassified so that Panetta could make the public remarks. The officials added that the Pentagon is particularly concerned about the growing Iranian cyber capabilities, as well as the often discussed threats from China and Russia. The two officials spoke on condition of anonymity because they were not authorized to discuss the cyberthreats publicly.

In his speech, Panetta said the Shamoon virus replaced crucial system files at Aramco with the image of a burning U.S. flag, and also overwrote all data on the machine, rendering more than 30,000 computers useless and forcing them to be replaced. He said the Qatar attack was similar.

Panetta offered no new details on the Pentagon’s growing cyber capabilities or the military rules of engagement the department is developing to guide its use of computer-based attacks when the U.S. is threatened.