In an afternoon statement, Trump wrote the country would continue showing "compassion to those fleeing oppression."
"America has always been the land of the free and home of the brave," he wrote. "We will keep it free and keep it safe, as the media knows, but refuses to say."
He pushed back on criticism suggesting his executive order amounts to the "Muslim ban" he proposed as a candidate.
"To be clear, this is not a Muslim ban, as the media is falsely reporting," he wrote. "This is not about religion -- this is about terror and keeping our country safe."
The statement is the latest attempt by Trump's White House to explain the controversial order, which the President signed at the Pentagon on Friday. The move halted US refugee entry into the US for 120 days, and barred all citizens of seven predominantly Muslim nations from entering the US for three months.
Trump cast the move as in line with the previous administration's moves to combat terrorism, writing: "My policy is similar to what President (Barack) Obama did in 2011 when he banned visas for refugees from Iraq for six months."
While Obama did order his administration to pause consideration of Iraqi refugee applications for six months in 2011, Trump's action is far more sweeping, preventing all citizens of Iraq from entering the United States for 90 days. The other nations under the same restrictions are Iran, Libya, Somalia, Sudan, Syria and Yemen.
Trump, in his statement Sunday, wrote those countries "are the same countries previously identified by the Obama administration as sources of terror."
Obama's administration, however, did not issue an outright ban on citizens of those countries entering the United States.
Trump said the US would "again be issuing visas to all countries once we are sure we have reviewed and implemented the most secure policies over the next 90 days."
And while he wrote: "I have tremendous feeling for the people involved in this horrific humanitarian crisis in Syria," Trump reiterated his primary focus was on US national security.
"My first priority will always be to protect and serve our country, but as President I will find ways to help all those who are suffering," he wrote.