The announcement follows a 90-day review period initiated as a follow-up to the administration's earlier travel ban.
"It's critically important that we know who is entering the United States," Secretary of Homeland Security Kirstjen Nielsen said in a statement. "These additional security measures will make it harder for bad actors to exploit our refugee program, and they will ensure we take a more risk-based approach to protecting the homeland."
The new, so-called "enhanced vetting measures" will affect refugees from the 11 countries deemed to warrant higher levels of scrutiny. The administration is not publicly identifying those countries, but according to the group Refugee Council USA, which represents refugee resettlement agencies and other non-governmental organizations, the list currently includes Egypt, Iran, Iraq, Libya, Mali, North Korea, Somalia, South Sudan, Sudan, Syria and Yemen.
A senior administration official who briefed reporters Monday said the move would "improve our ability to detect terrorists, criminals, and other nefarious actors."
"For instance, Secretary Nielsen directed US Citizenship and Immigration Services to conduct even more in-depth interviews of US refugee admissions programs applicants and family members from these countries, among other security measures," the official said. "And by more fully exploring refugee applicant backgrounds and verifying claims, we believe we will be able to bolster national security, and it will more effectively allow us to prevent fraud and identify national security risks."
The official did not detail specific measures, which will be implemented on a rolling basis, saying authorities "don't want to give the playbook to our enemies."
In October, when the review period was announced, the administration said it would be increasing screening of biographical data, social media and information sharing between agencies to better vet refugees' backgrounds. The administration is also planning to reexamine its list of high-risk countries, which was put in place during the Obama administration, to ensure it accurately reflect changes in the global threat environment.
Under the new policy outlined Monday, the secretaries of homeland security and state will review the list every six months and make changes as necessary.
The United States has admitted approximately 6,500 refugees since the fiscal year began in October, compared with about 32,000 during the same period last year, according to State Department data.
Of these, 332 refugees admitted so far this fiscal year came from the 11 high-risk countries, compared to nearly 16,000 in the same period last year.