The top of the 105-storey Ryugyong Hotel, the highest building under construction in North Korea, is seen in Pyongyang, North Korea early October 9, 2015. North Korea is getting ready to celebrate the 70th anniversary of the founding of its ruling Workers' Party of Korea on October 10.

A soldier walks on the bank of the river in central Pyongyang, North Korea April 16, 2017.

A general view shows a metro station in Pyongyang, North Korea August 14, 2005. Picture taken August 14, 2005.

Spectators watch people use The Munsu Water Park in Pyongyang in this undated photo released by North Korea's Korean Central News Agency (KCNA) October 16, 2013.

General view of the May Day Stadium undergoing remodelling in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang June 20, 2014.

A general view of the Daedong River Fish Market Restaurant in Pyongyang is seen during its opening, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang July 30, 2018.

The Ryugyong Kimchi Factory.

Solar panels face the sun from balconies of an apartment building in Mangyongdae District, Pyongyang August 27, 2014. In a country notorious for a lack of electricity, many North Koreans are taking power into their hands by installing cheap household solar panels to charge mobile phones and light up their homes. Picture taken August 27, 2014.

A picture of North Korea's founder Kim Il-sung decorates a building in the capital Pyongyang early in this October 5, 2011 file photo.

Children attend the 7th Congress of the Korean Children's Union (KCU) at the April 25 House of Culture in Pyongyang June 6, 2013 in this photo released by North Korea's Korean Central News Agency (KCNA) June 7, 2013.

A man walks in front of a replica of Unha-3 rocket displayed at the Sci-Tech Complex in Pyongyang, North Korea April 17, 2017. REUTERS/Damir Sagolj

People take part in the celebrations for the National Liberation Day near the Arch of Reunification in the city of Pyongyang, North Korea August 14, 2005. Picture taken August 14, 2005. Image used for illustrative purpose.

Fireworks explode in the sky over high rise buildings in Pyongyang in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang January 1, 2015.

Soldiers walk in front of the Monument to the Foundation of the Workers' Party in Pyongyang, North Korea April 16, 2017.

A member of staff looks from the balcony inside the Mangyongdae Children's Palace in central Pyongyang, North Korea May 5, 2016.

North Koreans celebrate the New Year by visiting statues of North Korea's founder Kim Il Sung and former leader Kim Jong Il at Mansudae hill in Pyongyang, in this January 1, 2014 photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang.

The Monument to the Foundation of the Workers' Party is photographed in Pyongyang, North Korea, October 11, 2015. Isolated North Korea marked the 70th anniversary of its ruling Workers' Party on Saturday with a massive military parade overseen by leader Kim Jong Un, who said his country was ready to fight any war waged by the United States.

Portraits of late North Korean leaders Kim Jong-il and Kim Il-sung (L) are lit at night in the North Korean capital of Pyongyang, July 24, 2013. REUTERS/Jason Lee

A newly built residential building is seen at sunrise in central Pyongyang, North Korea October 9, 2015. North Korea is getting ready to celebrate the 70th anniversary of the founding of its ruling Workers' Party of Korea on October 10.