The Travel Advisory index of the United States of America, which measures the safety of its citizens in other countries, has lowered Spain to level 4 (red), and the State Department has warned "Do not travel to Spain due to Covid-19” before adding "act more cautiously in the country due to terrorism and civil unrest."
From the Office of Consular Affairs it is reported that the US Centers for Disease Control and Prevention (CDC) have issued a health notice for trips to Spain due to "a very high level of Covid-19 in the country."
However, the notice is not an express prohibition and the CDC says that "before planning any international trip, the specific recommendations to be fully vaccinated are reviewed."
Regarding terrorism, the State Department claims that "armed groups continue to plot possible attacks in Spain" and may attack "with little or no warning, targeting tourist places, transportation hubs, markets, shopping centres, local government facilities, hotels, clubs, restaurants, places of worship, parks, major sporting and cultural events, educational institutions, airports and other public centres”, lists the US Government. The US authorities claim that "civil unrest" is "common" and "can take place in response to political or economic problems, on politically important holidays and during international events."
Spain shares this level 4 (red) warning with other European countries such as Portugal and the United Kingdom, while the US Consular Affairs Office has reviewed the situation in countries such as France, Italy and Greece, placing them at a 'level 3' to "reconsider" the possibility of travel.
The traffic light system has four levels that go from green (take the usual precautions) to red, that Spain now sits in.