He said he would prefer the United States to accept immigrants from countries like Sweden, Denmark and Norway.
Trump made the remarks during a speech at a rally in Pennsylvania.
A week earlier, the United States announced it had suspended all immigration applications, including applications for green cards and US citizenship, from Afghan migrants and nationals of 18 other countries.
Those countries, all non-European, include Afghanistan, Myanmar, Chad, the Republic of the Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan, Yemen, Cuba, Laos, Sierra Leone, Togo, Turkmenistan and Venezuela.
The official memo outlining the Trump administration’s new policy refers to last week’s attack on members of the US National Guard in Washington, in which an Afghan man was arrested as a suspect. Officials said they had identified Rahmanullah Lakanwal, a 29-year-old Afghan who had been granted asylum in April, as the suspect in the attack.
Since returning to power in January this year, President Donald Trump has adopted strict immigration policies. Following the recent attack on US soldiers in Washington, the Trump administration has intensified its actions against immigrants, particularly Afghans.