Kim Sang-duk, a 58-year-old US citizen also known as Tony Kim, was teaching accounting at the university.
"We have been informed that the USA government will no longer be allowing USA citizens to travel to (North Korea)", Young Pioneer Tours, which took the 22-year-old student to the country, also said on its website.
"The Secretary has authorized a Geographical Travel Restriction on all USA citizen nationals' use of a passport to travel in, through, or to North Korea", Nauert stated.
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Koryo Tours and Young Pioneers Tours both said that they had been informed by the government about the impending travel ban.
Before Warmbier's death, on May 25 the US Congress was presented a draft law banning tourist visits to North Korea for US citizens.
Sixteen Americans have been detained in the past decade in North Korea, including 22-year-old student Otto Warmbier who was given a long prison term for stealing a hotel propaganda banner.
"Since the United States does not maintain diplomatic or consular relations with North Korea, the USA government has no means to provide normal consular services to US citizens in North Korea", the advisory continued.
At least three Americans remained in North Korean custody.
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Turning to Simpson , Fromong said that if Simpson was released: "Juice I'll be here tomorrow for you". Simpson maintained he was not to blame and that his associates should also have served time.
Seoul's defence ministry had offered rare talks with the North at the Panmunjom truce village on the heavily militarised inter-Korean border to discuss tension reduction on Friday.
The State Department announced the decision late Friday morning, though two large travel agencies and anonymous USA officials indicated earlier that the ban would be coming.
U.S. President Donald Trump and Chinese President Xi Jinping agreed in April to produce tangible results on North Korea within 100 days.
Hundreds of Americans are among the roughly 4,000 to 5,000 Western tourists who visit North Korea each year, according to U.S. Representative Joe Wilson, a Republican from SC.
The United States last month had been "contemplating" a ban, Nauert said at the time. He had been sentenced to 15 years with hard labour for subversion. Last year North Korea allowed Chinese tourists to visit without passports, only increasing the volume of traffic.
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The US has in the past accused North Korea of detaining its citizens to use them as pawns in negotiations over its nuclear weapons programme.