President Donald Trump approved retaliatory military strikes against Iran on Thursday before changing his mind, US media report.
The New York Times, citing senior White House officials, says strikes were planned against a “handful” of targets.
They say the operation was allegedly under way “in its early stages” when Mr Trump stood the US military down. The White House has so far made no comment.
This comes after Iran shot down a US spy drone.
Tehran says the unmanned US aircraft entered Iranian airspace early on Thursday morning. The US maintains it was shot down in international airspace.
Tensions have been escalating between the two countries, with the US recently blaming Iran for attacks on oil tankers operating in the region. Iran has announced it will soon exceed international agreed limits on its nuclear programme.
Last year, the US unilaterally pulled out of a 2015 nuclear deal aimed at curbing Iran’s nuclear activities.