The US flew a rapid response team of Marines into Baghdad to reinforce its embassy after a mob of pro-Iranian demonstrators stormed the compound, setting fires and chanting "Death to America!"
"They will pay a very BIG PRICE! This is not a Warning, it is a Threat," wrote Trump, adding "Happy New Year!"
"We very much hoped that Iran would not miscalculate and confuse our restraint for weakness. But after so many attacks, it was important for the president to direct our armed forces to respond in a way that the Iranian regime will understand."