The Trump administration announced Monday it’s adding additional screening measures and restricting people who don’t have U.S. passports from entering the country if they have been in three African nations affected by a growing Ebola outbreak. 

At least 131 people are believed to have died from the latest outbreak of the virus in the Democratic Republic of Congo, health minister Samuel Roger Kamba said Tuesday. There has also been one death in neighboring Uganda, the Africa Centers for Disease Control and Prevention reported.

People without U.S. passports who have traveled to Congo, Uganda or South Sudan in the past three weeks will be restricted from entering the U.S., the Centers for Disease Control and Prevention announced.

The CDC also said the U.S. would enhance public health screening for people traveling from areas affected by the outbreak.

The travel order is among several measures announced by the CDC that take effect immediately and will be in effect for 30 days. The CDC said the travel order doesn’t apply to U.S. citizens, green-card holders or U.S. service members.

At least six Americans were exposed to Ebola virus in Congo, sources with international aid organizations told CBS News, although it was unclear if any had been infected. It also wasn’t immediately clear whether the Americans were still in Congo.

The agency also said it would try to identify people who have been exposed to the Ebola virus by coordinating with airlines, international partners and port-of-entry officials.

The CDC said the outbreak posed a low immediate risk to the U.S. general public.

“We will continue to evaluate the evolving situation and may adjust public health measures as additional information becomes available,” the CDC said.