It wasn't clear how many Americans the move will effect, as figures about how many Americans go to North Korea are difficult for even the US government to obtain.
The US strongly warns Americans against travelling to North Korea, but has not until now prohibited it despite other sanctions targeting the country. Americans who venture there typically travel from China, where several tour groups market trips to adventure-seekers.
Barring Americans from stepping foot in North Korea marks the latest US step to isolate the furtive, nuclear-armed nation, and protect US citizens who may be allured by the prospect of travelling there.
Nearly all Americans who have gone to North Korea have left without incident. But some have been seized and given draconian sentences for seemingly minor offences.
The travel ban comes as the Trump administration searches for more effective ways to ramp up pressure on North Korea over its nuclear weapons program.
Pyongyang's recent successful test of an intercontinental ballistic missile - the first by the North - has created even more urgency as the US seeks to stop North Korea before it can master the complex process of putting a nuclear warhead atop a missile capable of hitting the United States.
President Donald Trump has expressed frustration that his initial strategy - enlisting China's help and influence to squeeze the North economically and diplomatically - has not yielded major results.
Trump's administration is also considering other economic steps including "secondary sanctions" that could target companies and banks - mostly in China - that do even legitimate business with North Korea, officials said.
Under US law, the secretary of state has the authority to designate passports as restricted for travel to countries with which the United States is at war, when armed hostilities are in progress, or when there is imminent danger to the public health or physical security of United States travellers.
Geographic travel restrictions are rare but have been used by numerous administrations in the past for countries where it has been determined to be unsafe.
Since 1967, such bans have been imposed intermittently on countries such as Algeria, Iraq, Lebanon, Libya, Sudan, Cuba and North Vietnam. But the US doesn't currently prohibit its passports from being used to travel to any countries, even though financial restrictions limit US travel to Cuba and elsewhere.
If a passport ban were placed on North Korea, an American who violated it could face a fine and up to 10 years in prison for a first offence.
Warmbier, who died after being medically evacuated in a coma from North Korea last month, suffered a severe neurological injury from an unknown cause while in custody.
Relatives said they were told the 22-year-old University of Virginia student had been in a coma since shortly after he was sentenced to 15 years of hard labour in North Korea in March 2016.
He had been accused of stealing a propaganda poster while on a tour of the country.
Simon Cockerell, Beijing-based general manager of the Koryo Group, one of the leading organisers of guided tours to North Korea, said the ban would affect 800-1000 Americans who visit North Korea annually.
Although Pyongyang does not publish exact figures, Americans are thought to account for a mere 1 per cent of all foreign visitors.
Westerners make up 5 per cent of total visitors, Americans about 20 per cent of the Western contingent, according to statistics.
Cockerell said the ban would likely have a tangible impact on business for his and similar outfits, and said that would turn back the clock on engagement with the North.
"It's unfortunate because we criticise North Korea for being isolationist and now we're helping isolate them," Cockerell said. "That's not what soft power is about."
