The Pentagon says the United States launched airstrikes in Iraq, targeted by an Iranian-backed organization, possibly involved in an attack on a military base in Baghdad.
US officials say the US fighter jets targeted five destinations in Iraq that targeted Hezbollah's weapons installations.
The Defense Department statement said the attacks were carried out at five weapon warehouses to significantly reduce their potential for future attacks.
These attacks will increase tensions with Tehran and its proxies in Iraq, while Iran launched a large-scale missile attack on a US military base in Iraq two months ago.
Following the attacks, US defense officials threatened retaliation and made it clear that they knew who did it and the attackers would have to account.
US Secretary of Defense Mark Esper said: "The United States will not tolerate attacks against its own people, interests and our allies as we have demonstrated in recent months, we are defending our forces in Iraq and the region. Will take every necessary step. '
The Pentagon said in its statement that the installations targeted in the airstrikes were used to collect weapons used against the United States and its allies.
He called the counter-attack a 'direct response to the threat posed by the organization in defense, proportional and Iranian backing'.
US officials say the locations of the attacks were near Baghdad.
An American official said two attacks were carried out in Jarf al-Khair, one in Karbala, one in al-Masayb and one in Nawar Ahmed.
Authorities say the US hopes the casualties will be less than 50, and that the real effort was to target the weapons.
Paramilitary Popular Mobilization Units tell The Associated Press (AP) that two Iraqi federal police officers have been killed in Jarf al-Kheir.
The Iraqi military statement said that air raids on the 9th Division of the Popular Mobilization Units, Emergency Regiments and the Iraqi Army in Jarf al-Khair, al-Masayb, Najaf and Alexandria took place at about 1:30 pm.
Earlier, Mark Asper told the Pentagon that US President Donald Trump has given him the authority to take any necessary action.
"We will take action one step at a time, but we have to hold the culprits accountable, you cannot survive by attacking our base and killing and injuring Americans," he said.