The missile missed the drone and fell into the water, the official said.
Before the American MQ-9 drone took on the fire, she watched Iranian ships approach the tankers, the official added, though the source did not say whether the unmanned aircraft actually saw the boats attacking.
It is the first claim that the US has information about Iranian movements before the attack.
The same official also said that in the days leading up to the attack, a US Reaper drone in the Red Sea was shot down by what is believed to be an Iranian missile being fired by Houthi rebels.
The Pentagon had tough words on Iran on Friday as the US continues to claim that Tehran is responsible for attacking the two oil tankers in international waters following video footage allegedly showing that an Iranian patrol boat did not explode Mine removed from a ship's hull.
"We ensure that General McKenzie and the Central Command have the resources and support they need to carry out their missions," said Defense Secretary Patrick Shanahan, adding that the US is still working on an international one Consensus that Iran is behind the attack.
The United Kingdom released a statement on Friday stating that "almost certain" was that a section of the Iranian military ̵
The IRGC is an elite wing of the Iranian military that was founded after the events of the country revolution in 1979. In April 2019, the US officially designated it as a foreign terrorist organization, a move that was rejected by the authorities in Tehran ,
No other state or non-state actor "could have plausibly blamed it," the statement said.
However, Iran does not appear to be retreating and continues to show provocative behavior, according to a US official who told CNN on Friday that Iranian small boats are preventing tugs from hauling away one of the damaged tankers.
President Donald Trump seems to be convinced that Tehran was responsible.
"Iran did it and you know they did it because you saw the boat," he said, seeming to refer to the images and videos released by the Pentagon late Thursday.