Michelle Bernier-Toth, head of the Office of Overseas Citizens Services, said the changes were made because few people understood the distinctions in the previous, broad rankings.
"I personally was tired of explaining the difference between a travel warning and a travel alert, even to some of my colleagues," she said. "We needed to make it more accessible to people, to make sure the information was more easily understood using plain language."
Under the new rankings, Level 1, the lowest advisory, signals a need to "exercise normal precautions" in places where there is no more than the usual risk involved in international travel. Canada and Australia are among the countries at Level 1.
Level 2 means "exercise increased caution" and applies to nations where there is a heightened safety risk. Many countries in Western Europe, where there have been terrorist attacks in recent years, are listed as Level 2. Antarctica is also Level 2.
Level 3 translates bluntly as "Reconsider travel," with the recommendation to avoid going to countries with serious risks. Turkey, Russia and Venezuela are considered Level 3.
Level 4 is for countries with a "greater likelihood of life-threatening risks" in which the U.S. government may be very limited in its ability to help. Travelers already in those countries are advised to leave as soon as it is safe.
Eleven countries received the "Do not travel" recommendation, most in Africa and the Middle East — Mali, Central African Republic, Libya, South Sudan, Somalia, Yemen, Syria, Iraq, Iran, Afghanistan and North Korea.
In addition, the new system will explain why the advisory was made, using one-letter logos: C for crime, T for terrorism, U for civil unrest, H for health risks, N for natural disasters, E for special events such as an election or O for some other reason.
U.S. citizens are not banned from traveling to Level 4 countries. The one exception is North Korea, where the State Department has prohibited citizens from using their U.S. passports to visit without first obtaining a waiver.
Cuba is listed as Level 3, though last year a travel warning advised Americans against visiting. Most U.S. diplomats have been ordered to leave the country over concerns they were targeted for attacks, but Bernier-Toth said the reason Cuba was not listed as a Level 4 was that it still has not been determined what caused embassy personnel to suffer hearing and brain injuries.
In some countries, U.S. embassy personnel are restricted from visiting particular states or provinces where the risks are considered higher. The State Department calls it the no-double-standard principle.
"We let people know what restrictions we've imposed on ourselves," Bernier-Toth said.
In the past, governments of countries for which the State Department has issued travel warnings have complained vociferously, usually out of concerns about their tourism industry. Bernier-Toth said U.S. embassies were given the new rankings ahead of time so they could notify the governments of the impending changes.