Hyundai has invested millions of dollars in the park, which is one of the only examples of cooperation between the two Koreas.

But Yoo's arrest and increasingly hostile relations between North and South Korea have cast doubt on the facility's future.

His detention had sparked protest rallies in South Korea with demonstrators denouncing the North. 

Yoo's release follows a high-profile visit to North Korea last week by Bill Clinton, the former US president, who secured the freedom of two US journalists accused of illegally entering the country.

The two Koreas are technically still at war after the 1950-53 Korean conflict ended in a truce, not a peace treaty.