U.S. military cyber forces launched a strike against Iranian military computer systems Thursday as President Donald Trump backed away from plans for a more conventional military strike in response to Iran’s downing of a U.S. surveillance drone, U.S. officials said Saturday.

Two officials told The Associated Press that the strikes were conducted with approval from Trump. A third official confirmed the broad outlines of the strike. All spoke on condition of anonymity because they were not authorized to speak publicly about the operation.

The cyberattacks, a contingency plan developed over weeks amid escalating tensions, disabled Iranian computer systems that controlled its rocket and missile launchers, the officials said. Two of the officials said the attacks, which specifically targeted Iran’s Islamic Revolutionary Guard Corps computer system, were provided as options after two oil tankers were attacked earlier this month.

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The IRGC, which was designated a foreign terrorist group by the Trump administration earlier this year, is a branch of the Iranian military.

The action by U.S. Cyber Command was a demonstration of the U.S.’s increasingly mature cyber military capabilities and its more aggressive cyber strategy under the Trump administration. Over the last year, U.S. officials have focused on persistently engaging with adversaries in cyberspace and undertaking more offensive operations.

There was no immediate reaction Sunday morning in Iran to the U.S. claims. Iran has hardened and disconnected much of its infrastructure from the internet after the Stuxnet computer virus, widely believed to be a joint U.S.-Israeli creation, disrupted thousands of Iranian centrifuges in the late 2000s.

Tensions have escalated between the two countries ever since the U.S. withdrew last year from the 2015 nuclear deal with Iran and began a policy of “maximum pressure.” Iran has since been hit by multiple rounds of sanctions. Tensions spiked this past week after Iran shot down an unmanned U.S. drone, an incident that nearly led to a U.S. military strike against Iran on Thursday evening.

The cyberattacks are the latest chapter in the U.S. and Iran’s ongoing cyber operations targeting the other. Yahoo News first reported the cyber strike.

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