SEOUL -Some daring American globetrotters have brought forward their trips to North Korea to beat a travel ban effective from Friday (Sept 1), reported CNN.

With one key source of the badly-needed foreign currency drying up, North Korea has launched a new international marathon in October to fill its coffers, reported South Korean media.

Beginning Sept 1, US passports will be invalid for travel to the hermit kingdom and Americans in the country should leave before that date, said the US State Department earlier this month (Aug).

The decision is being put forth as a measure to ensure Americans' safety amid worsening relations between Washington and Pyongyang, said the US government. It cited the risk of "long-term detention" for US citizens who travelled to North Korea.

North Korea is currently holding two Korean-American academics, reported Reuters.

The travel ban was issued after the mysterious death of Otto Warmbier, a 22-year-old college student from Ohio who was imprisoned for nearly a year and a half, and returned to US in June in a coma from which he never woke up.

The ban comes at a time of heightened tensions between the United States and North Korea, which on Wednesday (Aug 30) threatened to fire more missiles into the Pacific. It fired a intermediate-range ballistic missile over Japan on Tuesday in a major escalation of tensions, In response, US President Donald Trump said that "all options" are again on the table.

But for Nicholas Burkhead and others like him, the threat of arrest and imprisonment in the totalitarian state is not a deterrent, nor is the looming threat that Pyongyang could become the staging ground for an armed conflict.

"With the upcoming travel ban I felt like it was now or never," said Virginia resident Burkhead, who lamented that he had run out of time to learn the Korean language before the travel ban.

CNN reported on Aug 28 that tourism to North Korea continues though a recent flight was a little emptier than usual. There were eight Americans on board, among the last to be allowed in under tourist visas before the ban, it reported.

"It's a pity for anyone curious to go, but especially for North Koreans who might want to know what American visitors are really like," said Simon Cockerell, who was on the flight.

Cockerell is the general manager of Beijing-based Koryo Tours, which specialises in helping tourists get to North Korea. It was Cockerell's 165th trip to the reclusive country.

Now that the communist state has been slapped with even tougher international sanctions over its nuclear and missile programme, the regime is increasingly turning to tourism as a source of foreign currency.

Uri Tours, a travel agency specialising in trips to North Korea, said North Korea will add a second marathon for foreigners in October, , reported Korea Times.

North Korea has been holding the "Mangyondae Prize International Marathon" since 1981 to mark state founder Kim Il Sung's birthday in April.

From 2014, the Kim Jong Un regime started allowing foreigners to participate, largely to make foreign money through the competition.

The Korea Chamber of Commerce and Industry said this year's event on April 9 attracted more than 1,100 marathoners from 50 countries, including Germany, the United States and China.

The US State Department does not track the number of American travellers to North Korea, but some estimates put it at about 1,000 each year. That amounts to a fifth of the total number of Western travellers who annually head to one of the world's most inaccessible countries, reported Foreign Policy website.

Independent travel to North Korea is not permitted, so those wanting to visit must book a tour through a travel agency that works with North Korean counterparts.

North Korea has condemned the US government for imposing a travel ban on the country, pledging that its doors would remain open for visiting Americans.

"We will always leave our door wide open to any US citizen who would like to visit our country out of goodwill and to see the realities with their own eyes."

The cash-strapped regime relies on foreign currency for business deals with its neighbour and main ally China and to purchase raw materials from abroad. Coal exports to China, North Korea's largest trade partner, are thought to be the country's greatest source of foreign currency, according to Radio Free Asia.

North Korea has also sent its workers to Russia, China, and places farther afield such as the Middle East and Africa for years, requiring them to remit much of their earnings to the government, which is believed to use the cash to fund its illicit weapons programmes.