Pyongyang, which has rattled the international community with its nuclear and missile tests in recent months, has agreed to send athletes to the Games and march with the South under one flag at the opening ceremony.
But the North has also vowed to press ahead with commemorations marking the 70th anniversary of the founding of its military, with the South's Yonhap news agency reporting that it is planning a major parade on February 8 -- a day before the Olympic opening ceremony.
"We believe the North will hold a military parade on February 8th to mark the anniversary of the birth of its regular forces", the source was quoted as saying.
A South Korean defence ministry spokesman said the ministry does not comment on "any matters of military intelligence".
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While North Korea often holds military parades to mark a variety of anniversaries, the country varies the dates it marks from year to year.
In 2017, leader Kim Jong-Un staged a giant spectacle showcasing a range of weaponry, including what appeared to be a new intercontinental ballistic missile (ICBM), in an event on April 15 marking the 105th anniversary of the North's founder.
He also used the speech to offer to take part in the South's Pyeongchang Games, billed by Seoul as a "Peace Olympics", which will be held some 80 kilometers (50 miles) from the heavily fortified border.
The outlook for the sporting extravaganza has brightened since North Korea confirmed its participation, easing security concerns over nuclear-armed Pyongyang.