North Korea appears to have staged a military parade in Pyongyang in the early hours of Thursday, the South's Yonhap news agency reported, citing an unnamed military source and saying Seoul was seeking to confirm the event.
Yonhap's source said only that there were "signs" the parade took place after midnight and was unable to provide additional details, such as whether leader Kim Jong Un was in attendance or if Pyongyang unveiled any new military hardware.
"The (South Korean) military is analysing those signs," the source told Yonhap.
South Korea's defence ministry did not immediately reply to an AFP request for confirmation or comment.
Thursday marks the 73rd anniversary of North Korea's founding.
The North last staged a military parade in January, days before the inauguration of US President Joe Biden, at which it showed off a new submarine-launched ballistic missile.
Pyongyang is under multiple sets of international sanctions over its banned nuclear weapons and ballistic missile programmes.
At the same time, it is under a self-imposed coronavirus blockade, having closed its borders to protect against the virus that first emerged in neighbouring China, adding to the pressure on its moribund economy.
Last month, the UN atomic agency (IAEA) said the nuclear-armed North appears to have started its plutonium-producing reprocessing reactor at Yongbyon, calling it a "deeply troubling" development.