President Donald Trump on Tuesday blamed Iran for planning an attack on the U.S. Embassy in Iraq and promised to hold Tehran "fully responsible."

"Iran killed an American contractor, wounding many. We strongly responded, and always will," the president wrote on Twitter. "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!" he added.

trump tweet

Later Tuesday, Trump amplified his harsh words for Iran. "This is not a Warning, it is a Threat," the president tweeted. "Happy New Year!"

trump tweet 2

Iran denied it was behind the violent protests and warned against any retaliation. "American officials have the astounding audacity of attributing to Iran the protests of the Iraqi people against (Washington's) savage killing of at least 25 Iraqis ...," Iranian Foreign Ministry spokesman Abbas Mousavi said in a statement carried on a ministry website.

Trump's tweets came after dozens of angry Iraqi Shiite militia supporters stormed the U.S. Embassy compound in Baghdad and set fire to a reception area on the grounds earlier in the day.

The Iraqi supporters, many dressed in military apparel, pushed into the compound using cars to break through its gate. The protesters hung a poster on the wall saying, "America is an aggressor."

Though the mob stopped short of entering the main building of the compound, many shouted "Down, Down, USA!" and flung water and rocks over the embassy walls. About 30 Iraqi soldiers in armored vehicles arrived near the embassy hours after the violence, according to an Associated Press report.

The attack followed deadly U.S. airstrikes on Sunday that killed 25 fighters of the Iran-backed militia in Iraq, carried out in retaliation for last week's killing of an American contractor in a rocket attack on an Iraqi military base that American officials blamed on the militia.

"The President is in close touch with his national security team and is receiving regular updates," said White House Press Secretary Stephanie Grisham. "As the President said, Iran is orchestrating this attack and they will be held fully responsible. It will be the President's choice how and when we respond to their escalation."