PYEONGCHANG (South Korea) — Security is a top concern at every Olympics, where athletes and fans in scattered venues can be difficult to protect. But rarely do they take place in the shadow of a nuclear standoff, as is the case with the Winter Games that open next week in South Korea.

Nearly 3,000 athletes from 92 nations and 100,000 spectators per day are expected to converge on the area around Pyeongchang, 50 miles (80 km) from the North Korean border, for what organisers say will be the largest-ever Winter Games. The South has mobilised tens of thousands of security personnel - including 50,000 soldiers - in what may be the most militarised security force in Olympic history.

A last-minute diplomatic breakthrough in which North Korea agreed to participate in the games has pushed fears of worst-case scenarios into the background, at least for now. But the North remains the most unpredictable factor in security arrangements, because it has a history of engaging in violence when South Korea hosts international sports events.

The arrival Thursday (Feb 1) of a delegation of North Korean athletes - part of a larger contingent of around 500 athletes, officials and performers - raises a separate set of security challenges, including protecting them from attacks by extremists in South Korea.

Organisers have long feared that the North might test a missile or nuclear weapon during the games, perhaps even provoking a chain reaction of escalations leading to war. Such worries have subsided since the January deal, in which the two Koreas agreed to march under one flag in the opening ceremony.

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 Mr Yoo Dong-ryul, 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 Mr 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, organisers have scrambled to coordinate security and logistics for its delegation, which includes a cheerleading squad.

Mr 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, Mr 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. Police quickly extinguished the fire to avoid angering the visitors, who accord Mr Kim an almost godlike status.

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.

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, organisers 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, 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.” THE NEW YORK TIMES