North and South Korea have been talking since last week - for the first time in more than two years - about the Olympics, offering a respite from a months-long standoff over Pyongyang's pursuit of nuclear and missile programmes, although Japan urged caution over the North's "charm offensive".
The two Koreas will compete as a unified team in the Olympics for the first time, though they have joined forces at other international sports events before.
North Korea will send a delegation of more than 400, including 230 cheerleaders, 140 artists and 30 Taekwondo players for a demonstration, a joint press statement released by Seoul's unification ministry said, adding the precise number of athletes will be hammered out after discussions with the IOC.
Prior to the Games, the sides will carry out joint training for skiers at the North's Masik Pass resort and a cultural event at the Mount Kumgang resort, for which Seoul officials plan to visit the sites next week.
The delegation is expected to begin arriving in South Korea on Jan. 25, the statement said.
The North will separately send a 150-strong delegation to the Paralympics.
Twenty nations meeting in the Canadian city of Vancouver agreed on Tuesday to consider tougher sanctions to press North Korea to give up its nuclear weapons and U.S. Secretary of State Rex Tillerson warned the North it could trigger a military response if it did not choose dialogue.
Japanese Foreign Minister Taro Kono said the world should not be naive about North Korea's "charm offensive" over the Olympics.
"It is not the time to ease pressure, or to reward North Korea," Kono said. "The fact that North Korea is engaging in dialogue could be interpreted as proof that the sanctions are working."
North Korean leader Kim Jong Un has refused to give up development of nuclear missiles capable of hitting the United States in spite of increasingly severe U.N. sanctions, raising fears of a new war on the Korean peninsula. The North has fired test-fired missiles over Japan.
In state media this week, the North warned the South of spoiling inter-Korean ties by insisting it gives up its nuclear weapons.
"We will work actively to improve North-South Korean relations but will not stand still to actions that are against unification," the North's Rodong Sinmun newspaper said.
The South's Unification Ministry said the two sides exchanged opinions on several issues, including the size of the North Korean athletics team and joint cultural events.
Seoul has proposed a joint ice hockey team, which triggered an angry response from athletes in the South suddenly being told they may have to play alongside total strangers.
"I don't know if it will happen, but a joint team will be a good opportunity for ice hockey to shed its sorrow as a less-preferred sport as many Koreans will take interest," South Korean President Moon Jae-in told players during a visit to a training centre.
The number of petitions to the presidential Blue House's website opposing a unified team climbed to more than 100 this week, with the most popular petition gaining more than 11,000 votes.
"This isn't the same as gluing a broken plate together," said one of the signers.
Paik Hak-soon, the director of the Centre for North Korean studies at Sejong Institute in South Korea, said North Korea was using the cheering squad to draw attention to its apparent cooperative spirit.
"Seeing good results in competitions thanks to the cheering squad would enable the North Koreans to say they contributed to a successful Olympics and the South Korean government would likely agree," said Paik.
"In the end, they are using this old tactic to get to Washington through Seoul."
On Tuesday, officials from North and South agreed a 140-person North Korean orchestra would perform in South Korea during the Games. Pyongyang is also planning to send a large delegation in addition to the athletes and orchestra.
Reclusive North Korea and the rich, democratic South are technically still at war because their 1950-53 conflict ended in a truce, not a peace treaty. The North regularly threatens to destroy the South, Japan and their major ally, the United States.
China, which did not attend the Vancouver meeting, said on Wednesday the gathering showed a Cold War mentality and would only undermine a settlement of the North Korea problem.
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