Iran has launched dozens of ballistic missiles at US targets throughout Iraq, including Erbil in northern Iraq and the al-Assad air base in the west of the country.
Iran’s Revolutionary Guard has confirmed it is behind the attacks in revenge for the killing of General Qassem Soleimani and has warned the US and regional allies against retaliating.
The Guard is reportedly calling the attack Operation Martyr Soleimani.
It is not yet known if there are any deaths or casualties, or how much damage has been done.
Following the attack, supreme leader to the secretary of the supreme national security council in Iran, Saeed Jalili posted an image of the Iranian flag, mirroring a similar tweet by Mr Trump.
The president had posted a picture of the US flag after the drone strike which killed Gen Soleimani on Friday.
The White House said earlier this evening that Mr Trump had been briefed about the attacks and had gone to the Situation Room, with it initially understood he would be addressing the nation.
However, this was later denied by White House spokeswoman Stephanie Grisham and instead the president took to Twitter to say “all is well” and that the US has the “most powerful and well equipped military” in the world.
He said: “All is well! Missiles launched from Iran at two military bases located in Iraq. Assessment of casualties & damages taking place now. So far, so good! We have the most powerful and well equipped military anywhere in the world, by far!