“Iran is a state sponsor of terrorism. Iran regularly fails to cooperate with the United States Government in identifying security risks, is the source of significant terrorism around the world, and has historically failed to accept back its removable nationals,” the announcement said late on Wednesday.
"The countries that we have (on the travel ban list) don't have things under control," Trump told reporters in the White House on Thursday.
"And why now? I can say that it can't come soon enough frankly. We want to keep bad people out of our country."
The US State Department designated the Islamic Republic a state-sponsor of terrorism in 1984. However, the latest statement against Iran comes amid sensitive nuclear negotiations between Washington and Tehran.
Effective June 9, the directive prohibits most travelers from Afghanistan, Myanmar, Chad, Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan, and Yemen from entering the United States. Partial travel restrictions have also been imposed on citizens from seven additional countries: Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan, and Venezuela.