The US is to ban its citizens from travelling to North Korea.
State Department spokeswoman Heather Nauert said in a statement that the ban would be published next week in the Federal Register, to come into effect 30 days later.
US officials linked the move to the death of jailed American student Otto Warmbier.
Once the ban is in effect, US citizens will need special validation to travel to or within North Korea.
Mr Warmbier travelled to North Korea with Young Pioneer Tours. He was arrested in 2016 for trying to steal a propaganda sign and sentenced to 15 years in prison. He was returned to the US in a coma in June and died a week later.
Koryo Tours and Young Pioneer Tours, who both operate in North Korea, revealed on Friday that they had been told of the upcoming ban by the Swedish embassy, which acts for the US as Washington has no diplomatic relations with Pyongyang.
Rowan Beard, of Young Pioneer Tours, told the BBC the embassy was urging all US nationals to depart immediately.
He said the embassy was trying to check on the number of US tourists left in the country.
Ms Nauert’s statement said: “Due to mounting concerns over the serious risk of arrest and long-term detention under North Korea’s system of law enforcement, the Secretary has authorised a Geographical Travel Restriction on all US nationals’ use of a passport to travelling through, or to North Korea.
“Once in effect, US passports will be invalid for travel to, through, and in North Korea, and individuals will be required to obtain a passport with a special validation in order to travel to or within North Korea.
“We intend to publish a notice in the Federal Register next week.
“The restriction will be implemented 30 days after publication.”
Rowan Beard said that the 30-day grace period would “give leeway for any [Americans] currently in the country as tourists or on humanitarian work”.
Simon Cockerell of Koryo Tours told the BBC the agency would still conduct tours and take Americans until the ban came into effect.
“If their country allows them to go, we will take them,” he said.
Mr Cockerell added: “It’s unfortunate for the industry but also for North Koreans who want to know what Americans are really like.”
After the death of Mr Warmbier, the China-based Young Pioneer Tours announced it would no longer take visitors from the US to the country.
There has been movement towards a ban for a while in the US, which increased with the Warmbier death.
In May, two congressmen introduced the North Korea Travel Control bill to cut off the foreign currency the country earns from American tourists.
The House foreign affairs subcommittee is scheduled to take up the draft legislation on 27 July but it would still have to go to the Senate. So there could be an executive order.
Apart from the treatment of Americans in North Korea, tension has been increasing over Pyongyang’s nuclear programme.
This month North Korea announced it had successfully tested what it said was its first intercontinental ballistic missile (ICBM), the latest in a series of tests in defiance of a UN ban.
Its range has been disputed, but some experts said it could reach Alaska.
The US and South Korea then conducted a ballistic missile drill and issued a stark warning to the North.
Some are suggesting the US is using the date the ban is set to be announced – 27 July – to cloud North Korea’s Victory Day on the same day.
North Korea only relaxed its rules for American visitors in 2010.
The state department does not keep a record of the number of American tourists.
Tour operators suggest that up to 1,000 visit every year.
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