North Korea held a military parade on Monday night to mark the 90th anniversary of the founding of the country's army, a South Korean military source said, amid fears it would conduct provocations directed against the United States on the day.

The United States, Japan and South Korea strengthened surveillance on North Korea as concern mounted that Pyongyang might launch an intercontinental ballistic missile or carry out its seventh nuclear test on the occasion of the anniversary.

South Korean media reported Sunday that the North showed signs of holding a vast military parade in Pyongyang on the anniversary of the founding of the Korean People's Revolutionary Army, the predecessor of the present Korean People's Army.

North Korean national flags are displayed in Pyongyang on April 25, 2022, to celebrate the 90th anniversary of the founding of the country's military. (Kyodo)

April 25, 1932, is the day that North Korea says its founder Kim Il Sung, the grandfather of current leader Kim Jong Un, started organizing an anti-Japanese guerrilla force.

The latest military parade, during which Kim Jong Un may have made a speech, is expected to be broadcast by the official Korean Central Television on Tuesday.

North Korea refrained from nuclear and ICBM tests as well as a military parade on April 15, the 110th anniversary of the birth of Kim Il Sung -- the nation's biggest holiday known as the "Day of the Sun." The country usually stages larger celebrations on every fifth and 10th anniversary.

On March 24, North Korea made the first launch of an ICBM since November 2017, marking an end to its self-imposed moratorium on intercontinental ballistic rocket firings since April 2018.

Pyongyang said earlier this year that it may restart all "activities" it had temporarily suspended to build trust with former U.S. President Donald Trump, President Joe Biden's predecessor, while urging Washington to drop its "hostile policy."

North Korea's state-run media, meanwhile, said Friday that Kim Jong Un and outgoing South Korean President Moon Jae In exchanged personal letters and shared the view that inter-Korean ties "would improve" if the North and South "make tireless efforts with hope."

The report came just days after South Korea and its defense ally, the United States, began their joint springtime military exercises, which the North slammed as a "rehearsal" for war.

However, speculation lingers that in the near future, Pyongyang might stage a nuclear test or launch an ICBM capable of delivering a nuclear warhead to anywhere in the continental United States.

On April 17, the official Korean Central News Agency reported Kim Jong Un observed the test-firing of a "new-type tactical guided weapon" the previous day. Some analysts say it can carry a tactical nuclear weapon that could be used in a limited strike.

The United States and North Korea remain technically in a state of war as the 1950-1953 Korean War, in which U.S.-led U.N. forces fought alongside South Korea against the North supported by China and the Soviet Union, ended in an armistice, not a peace treaty.