U.S. President Donald Trump blamed Iran on Tuesday for "orchestrating" an attack on the U.S. Embassy in Baghdad and said he would hold Tehran responsible, as officials said more Marines were expected to be sent to the mission.

"Iran killed an American contractor, wounding many. We strongly responded, and always will. Now Iran is orchestrating an attack on the U.S. Embassy in Iraq. They will be held fully responsible. In addition, we expect Iraq to use its forces to protect the Embassy, and so notified," Trump said on Twitter.

"To those many millions of people in Iraq who want freedom and who don't want to be dominated and controlled by Iran, this is your time!" Trump wrote in another Twitter post.