Rows of military bands and goose-stepping and sword-wielding soldiers marched through Pyongyang's main Kim Il-sung square for the "Day of the Sun" celebrations, as a black-suited Kim Jong-un watched.
"It's presumed to be a new ICBM", a Seoul official was quoted as saying by Yonhap News Agency.
Military vehicles carry missiles with characters reading "Pukkuksong" during the military parade in North Korean marking the 105th birth anniversary of country's founding father, Kim Il Sung.
The North's Korean People's Army (KPA) added its voice to the bellicose rhetoric on Friday with a statement threatening strikes against USA military bases and other targets in South Korea.
If North Korea holds a military parade, it is expected to showcase its latest missiles and other new military equipment to flex its military muscle.
During an interview with the Associated Press on April 14, North Korean Vice Minister Han Song-ryol said that the North "will go to war" if the USA makes that choice.
North Korea has continued to break its global obligations by test-firing ballistic missiles despite being hit with two rounds of United Nations sanctions after a pair of nuclear tests in 2016 alone.
The United States was reportedly ready to strike North Korea if US officials became convinced the country would carry out its test, and the Trump administration said its "strategic patience" with the country has run out. Also on display was a powerful midrange missile that outside analysts call a "Musudan", and which can potentially reach USA air bases in Guam, as well as a new solid-fuel midrange missile that can be fired from land mobile launchers, making them harder to detect before launch.
Wang's comments Friday mark the latest attempt to cool tensions by North Korea's most important ally and key provider of food and fuel aid.More news: Kim's desire for peace 'deciding factor' in US-North Korea relations
It was also a bold display for enemies such as the United States. Any fighting on the Korean Peninsula is likely to draw in China, which has repeatedly expressed concerns about a wave of refugees and the possible presence of USA and South Korean troops on its border.
North Korea is thought to have a small arsenal of atomic bombs and an impressive array of short- and medium-range missiles.
Kim Jong-un reviews the parade featuring new long-range missiles. This would allow North Korea to prevent its limited number of ICBM-capable launcher trucks from being damaged during launches and also make the missiles harder to detect after they're fired, he said.
Other military hardware at the parade included tanks, multiple rocket launchers and artillery, as well as a solid-fuel missile created to be fired from submarines.
The North regularly launches short-range missiles, but is also developing mid-range and long-range missiles meant to target USA troops in Asia and, eventually, the US mainland.
There were no further details, and the office said it was analysing the launch.
"I don't think a strategy that relies on pressuring North Korea to give up its nuclear weapons is going to work", he told Fox News.
Air China and North Korea's Air Koryo are the only two airlines serving that route, with the latter operating on Mondays, Wednesdays and Fridays.
He then stepped up to a podium and clapped with senior government officials to address the thousands of soldiers and civilians taking part in the parade at Kim Il Sung Square in Pyongyang, the capital. South Korea has a spotty record of tracking developments in North Korea, as information about the secretive, authoritarian state is often impossible to confirm.