But there are still suspicions about the North’s intentions.
“North Korea will cause trouble one way or another in order to interrupt the successful completion of the Games,” said Yoo Dong-ryul, the head of the Korea Institute of Liberal Democracy in Seoul. “In all the years the Kim dynasty has been in power, North Korea has never once properly cooperated with South Korea.”
In November 1987, 10 months before Seoul hosted the 1988 Summer Games, North Korean agents detonated a bomb on a South Korean airliner, killing all 104 passengers and 11 crew members. The goal, one of the agents later told investigators, was to frighten international athletes and visitors out of attending the Games.
When South Korea co-hosted the soccer World Cup in 2002, a naval clash with North Korea in disputed waters killed six South Korean sailors just hours before the South played in the third-place match.
But the North did not take part in those sporting events. When North Korea has participated in events hosted by the South — the 2002 Asian Games in Busan and the 2014 Asian Games in Incheon, for example — there have been no major disruptions.
That is why South Korean officials and analysts argue that the risk of a military provocation during these Olympics — nuclear or otherwise — has been significantly reduced.
Still, South Korea plans to field up to 60,000 security personnel on each day of the Games, including the 50,000 soldiers — more than twice the number of military personnel deployed during the 2016 Summer Olympics in Rio de Janeiro.
“The possibility of a missile or nuclear test is extremely low,” said Shin Beom-chul, an expert on North Korea at the government-run Korea National Diplomatic Academy in Seoul. “The North may use the Games as a political propaganda opportunity to show that while they may be a nuclear power, they also want to have peace with their neighbors.”
Since North Korea agreed to attend the Games, organizers have scrambled to coordinate security and logistics for its delegation, which includes a cheerleading squad.
Jeong Se-yun, a provincial police official involved in the planning, said the North’s decision was a tremendous relief. “But it also created a lot more work for us,” he said. “I’ve barely slept in the last month. That’s why my eyes are always red now.”
One fear is that something might happen during the Games that could prompt North Korea’s leader, Kim Jong-un, to recall its athletes and retaliate in some way.
A small group of right-wing protesters burned an image of Mr. Kim as a North Korean delegation traveled through Seoul last month. The police quickly extinguished the fire to avoid angering the visitors, who accord Mr. Kim an almost godlike status.
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The state media in North Korea condemned the act as a “hideous crime” committed by “human rejects,” and warned that only South Korea would be to blame if the North withdrew from the Games.
There is also concern that a North Korean athlete or another member of the delegation might try to defect, putting the South Korean government in the difficult position of deciding whether to return the defector or anger the North.
Analysts said a defection during the Olympics would be highly unlikely because the North has almost certainly vetted its delegation carefully and would keep its people under close watch.
The authorities are also on alert against a cyberattack, either by the North or by Russia, whose delegation was banned from participating under the Russian flag in the Pyeongchang Games after revelations of systematic government-sponsored doping.
North Korea has developed sophisticated hacking capabilities and launched a series of damaging attacks around the world, including one in 2013 that temporarily knocked out three banks and two television networks in South Korea.
To combat more conventional threats, organizers said the security forces intended to deploy both old-fashioned checkpoints and new technologies such as facial recognition systems, smart cameras and drones. A tactical surveillance blimp will hover above.
South Korea is considered one of the world’s safest tourist destinations, with low crime rates and essentially no history of terrorist activity other than by the North. Nevertheless, the immigration authorities said last month that they had deported 17 foreign nationals believed to pose a terror risk, according to the Korea Times newspaper. Some of the deportees were said to be from Central Asia and Southeast Asia.
“Broadly, we consider the event low-risk,” the London-based Risk Advisory Group wrote in a recent analysis of the Pyeongchang Games. “Compared with the host cities of the most recent Winter and Summer Games in 2014 and 2016 respectively, Pyeongchang is a benign environment in terms of terrorism, crime and unrest.”
In the rural areas around Pyeongchang, the most commonly reported crime is drunken fighting.
Many residents shrugged off the idea that the North might attempt to disrupt the Games, which may reflect the fact that South Koreans have grown accustomed to living within range of its artillery and rockets. Even security officials sounded nonchalant, as if surprised by the world’s anxiety.
“We are well aware of the international community’s concerns about the safety of the Olympics due to threat of North Korean nuclear test and missile launches,” the interagency body established to handle Olympic security said in a statement in response to written questions. “Signs of North Korean provocation are monitored 24/7 through various means every day, regardless of the Olympics.”
The interagency body added that underground evacuation centers for up to 30,000 people had been prepared at an undisclosed site near Pyeongchang for use in the event of any sort of attack.
Other security measures include an emergency alert system that can send messages to all cellphones in the area, though it is unclear whether its operators are prepared for the tens of thousands of foreign visitors en route to Pyeongchang.
One recent morning an alert flashed on cellphones written only in Korean, causing a moment of panic among some non-Korean speakers, who immediately assumed the worst.
It turned out to be a warning to beware of fires because of dry weather.