While Iran appeared to be "standing down" from a military response, the cyber threat remains real, said analysts.
Despite early reports that no Americans were harmed, 11 U.S. service members did sustain injuries.
An official said details are still being worked out to restore the training of Iraqi forces.
Iran's president warned Wednesday that European soldiers in the Mideast “could be in danger.”
Iran's Judiciary spokesman Gholamhossein Esmaili said “some individuals" were arrested after “extensive investigations."
American troops were informed of an impending missile barrage hours before their air base in Iraq was struck by Iran.
Qasem Soleimani held Iran's highest military award and now has been awarded Syria's.
Tensions have soared since the U.S. airstrike earlier this month that killed Gen. Qassem Soleimani.
The leader of the Lebanese militant group Hezbollah is closely aligned with Iran.
In response to a question about whether Trump was “embellishing'' the threat, Esper said, ”I don't believe so.”