The U.S. government has cautioned Americans from traveling to North Korea, warning they may be subject to arrest or long-term detention.

In a latest travel warning, the department said that North Korea could regard Americans as spies if they enter the North without first having received explicit, official permission and a North Korean visa.

The department added that North Korean officials may view U.S. tourists’ unauthorized attempts to talk to a North Korean citizen or buy a North Korean product as espionage.

It explained that the U.S. and North Korea have not established diplomatic relations, and therefore, the U.S. government cannot provide consular services to U.S. citizens in North Korea. The department advised Americans to use the Swedish Embassy in Pyongyang when they visit North Korea.