North Korea has fired an unidentified projectile towards the sea off its east coast.
South Korea's Joint Chiefs of Staff did not immediately say on Monday whether the weapon was ballistic or how far it flew.
The launch followed an October 3 test of what the North described as a hypersonic intermediate-range missile designed to evade missile defences in South Korea and Japan.
North Korea in recent weeks has also conducted live-fire drills and commissioned a new warship as leader Kim Jong-un continues to flaunt his military nuclear program while rejecting US and South Korean offers to resume long-stalled diplomacy.
Tensions were further worsened after three South Korean soldiers were injured in land mine explosions last month near the heavily armed inter-Korean border.
The South's military and the US-led United Nations Command concluded the blasts were caused by devices planted by North Korea, which has denied responsibility and ridiculed the South's demands for an apology., the South Korean military said on Monday.
Japan's coast guard said the projectile, believed to be a North Korean ballistic missile, appeared to have already fallen.
The launch comes after South Korean President Lee Jae Myung oversaw the country's first test-firing of a domestically developed hypersonic missile last week.
with AP