Satellite images of luxury boats further suggest N.Korea's Kim at favoured villa

Wonsan also holds symbolic power for the Kim dynasty: It was there Kim Il Sung, who helped found North Korea at the end of Japanese colonial rule in 1945, first landed with Soviet troops to take over the country.

Wonsan is believed by some experts to be Kim Jong Un's birthplace, partly because he spent his early years at the family's palace there, although official history has never confirmed where he was born.

The Japanese chef Kenji Fujimoto, who worked for the Kims and visited Wonsan, recounted in his memoirs how a young Kim Jong Un described rollerblading, playing basketball, riding jet skis and playing in the pool at the compound.

Later, photos showed Kim sipping drinks there with American basketball player Dennis Rodman when the star visited North Korea in 2013.

The Wonsan area has also become emblematic of Kim's strategy for survival based on a combination of economic development, tourism, and nuclear weapons. He is rebuilding the city of 360,000 people and wants to turn it into a billion-dollar tourist hotspot.

In recent months, the project has been repeatedly delayed, undermined in part by international sanctions imposed over the North's nuclear and missile programmes, which have restricted its ability to seek foreign investment.

Wonsan has also been the scene of some of Kim's renewed military drills and missile tests, which he resumed amid increasing frustration with a lack of progress in denuclearisation talks with the United States and South Korea.