The attack crippled computers used to control rocket and missile launches.
The United States launched cyber attacks against Iranian missile control systems and a spy network this week after Tehran downed an American surveillance drone, US media reported on Saturday.
US President Donald Trump ordered a retaliatory military strike against Iran after the drone shootdown but then called it off, saying the response wouldn't be "proportionate" and instead pledged new sanctions on the country.
But after the drone's downing, Trump secretly authorized US Cyber Command to carry out a retaliatory cyber attack on Iran, The Washington Post reported.
The attack crippled computers used to control rocket and missile launches, according to the Post, which cited people familiar with the matter.
Yahoo cited two former intelligence officials as saying the US targeted a spying group responsible for tracking ships in the strategic Strait of Hormuz, where Washington has blamed Iran for two recent mine attacks on oil tankers.
The Post said the strikes, which caused no casualties, had been planned for weeks and were first proposed as a response to the tanker attacks.
US defense officials refused to confirm the reports.
"As a matter of policy and for operational security, we do not discuss cyberspace operations, intelligence or planning," Defense Department spokeswoman Heather Babb told AFP.
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