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.

Tensions are high between the US and Iran once again following Trump's move more than one year ago to leave a multinational accord curbing Iran's nuclear ambition.

His administration has instead imposed a robust slate of punitive economic sanctions designed to choke off Iranian oil sales and cripple its economy.

On Saturday, Trump said the US would put "major" new sanctions on Iran next week.

Tehran said it shot down the US drone on Thursday after it violated Iranian airspace -- something Washington denies.

Meanwhile, Iran has denied responsibility for the tanker attacks, and a top military official on Saturday pledged to "set fire to the interests of America and its allies" if the US attacks.

These cyber attacks aren't the first time the US and Iran have dueled online.

The Stuxnet virus, discovered in 2010, is believed to have been engineered by Israel and the US to damage nuclear facilities in Iran.

And Tehran is believed to have stepped up its own cyber capabilities in the face of US efforts to isolate the Islamic republic.