Sweden is reintroducing temporary border controls at ferry terminals, airports, road crossings with other countries, and other entry points to the Scandinavian nation due to a “a serious threat to public order and internal security.”

The Swedish government said the temporary controls would start immediately and last until Nov. 11, meaning travellers will have to show passports and visas during the six-month period.

The government did not mention a specific threat in its announcement but said the security situation in the country’s region of Europe is “extremely serious, and the overall terrorist threat level in Sweden remains elevated.”

Swedish Justice Minister Morgan Johansson noted that once inside Europe’s passport-free travel zone known as the Schengen Area, people can move relatively freely among 26 countries – 22 European Union nations plus Iceland, Liechtenstein, Norway, and Switzerland.

Normally, people and goods move freely between these countries without border checks. Temporary controls are allowed for security or health reasons, and several other Schengen countries, including Germany, Austria, Norway, and Denmark, have them in place, Johansson said.