The US plans to expand the number of countries covered by its travel ban to more than 30, US Homeland Security Secretary Kristi Noem said on Thursday.

Noem, in an interview on Fox News' "The Ingraham Angle," was asked to confirm whether the administration of President Donald Trump would be increasing the number of countries on the travel ban list to 32.

"I won't be specific on the number, but it's over 30, and the president is continuing to evaluate countries," she said.

Trump signed a proclamation in June banning the citizens of 12 countries from entering the United States and restricting those from seven others, saying it was needed to protect against "foreign terrorists" and other security threats.

The bans apply to both immigrants and non-immigrants, such as tourists, students and business travellers.

Noem did not specify which countries would be added to the list.

"If they don't have a stable government there, if they don't have a country that can sustain itself and tell us who those individuals are and help us vet them, why should we allow people from that country to come here to the United States?" Noem said.

Reuters previously reported that the Trump administration was considering banning citizens of 36 additional countries from entering the United States, according to an internal State Department cable.

An expansion of the list would mark a further escalation of migration measures the administration has taken since the shooting of two National Guard members in Washington, D.C., last week.

Investigators say the shooting was carried out by an Afghan national who entered the US in 2021 through a resettlement program under which Trump administration officials have argued there was insufficient vetting.

Days after the shooting, Trump vowed to "permanently pause" migration from all "Third World Countries," although he did not identify any by name or define "third-world countries."

Prior to that, officials from the Department of Homeland Security said Trump had ordered a widespread review of asylum cases approved under the administration of his predecessor, Democratic President Joe Biden and Green Cards issued to citizens of 19 countries.

Since returning to office in January, Trump has aggressively prioritized immigration enforcement, sending federal agents to major US cities and turning away asylum seekers at the US-Mexico border.

His administration has frequently highlighted the deportation push, but until now it has put less emphasis on efforts to reshape legal immigration.