The US has approved plans for a series of strikes on Iranian targets in Syria and Iraq.
The strikes will take place over a number of days, officials said, and weather conditions will likely dictate when they are launched.
It comes after a drone attack killed three US soldiers in Jordan, close to the Syrian border, on Sunday.
The US blamed an Iranian-backed militia group for that attack.
That group, the Islamic Resistance in Iraq, is believed to contain multiple militias that have been armed, funded and trained by Iran’s Revolutionary Guards force. It has said it was responsible for Sunday’s strike.
Iran, meanwhile, has denied any role in the attack which injured 41 other US troops at the military base, known as Tower 22.
US officials have said that US intelligence believes that the drone used to attack the facility was manufactured by Iran – and is similar to the drones Iran has been sending to Russia for its invasion of Ukraine.
At a news conference on Thursday, US Defence Secretary Lloyd Austin defended the delayed military response, saying: “We will respond where we choose, when we choose and how we choose.”