By Marnie Hunter, Sept. 28 (CNN) — Norway on Monday moved into the highest-risk category on the US Centers for Disease Control and Prevention's list of travel advisories for destinations around the world.

The Scandinavian country moved up to "Level 4: Covid-19 Very High" just as the country relaxed most of its domestic Covid-related restrictions over the weekend. Neighbors Sweden and Denmark are listed in the CDC's Level 3 category.

In Eastern Europe, Bulgaria also moved into the Level 4 category on Monday.

Destinations that fall into the "Covid-19 Very High" Level 4 category have had more than 500 cases per 100,000 residents in the past 28 days, according to CDC criteria.

People should avoid travelling to locations designated with a "Level 4" notice, the CDC recommends. Anyone who must travel should be fully vaccinated first, the agency advises. Nearly 90 destinations are now listed as Level 4.

Both Norway and Bulgaria were previously listed as "Level 3: Covid-19 High." The Level 3 category applies to destinations that have had between 100 and 500 cases per 100,000 residents in the past 28 days.

The CDC's travel notices range from Level 1 ("low") to Level 4 ("very high"). The CDC does not list the United States in its travel advisories.

The two new destinations added to Level 4 on September 27 are:

• Bulgaria
• Norway

New Level 3 destinations

Six destinations moved to Level 3 on September 27:

• Bangladesh
• Equatorial Guinea
• Panama
• Saint Barthelemy
• Singapore
• Slovakia

Three places moved down from Level 4: Bangladesh, Panama and Saint Barthelemy (St. Barts).

The other three moved up into the higher-risk Level 3 category. Equatorial Guinea moved up from a previous Level 1 designation, and Singapore and Slovakia moved up from Level 2.

Destinations carrying the "Level 2: Covid-19 Moderate" designation have seen 50 to 99 Covid-19 cases per 100,000 residents in the past 28 days.

You can view the CDC's risk levels for global destinations on its travel recommendations page.

In its broader travel guidance, the CDC has recommended avoiding all international travel until you are fully vaccinated.

"Fully vaccinated travellers are less likely to get and spread Covid-19. However, international travel poses additional risks, and even fully vaccinated travellers might be at increased risk for getting and possibly spreading some Covid-19 variants," the agency said.