North Korea has attempted to launch a missile on its east coast, but it is believed to have failed, South Korea's military says.
It comes a day after the state warned the US that it was "ready to hit back with nuclear attacks" amid mounting tension in the region.
"North Korea attempted to test an unidentified type of missile from [its eastern port of] Sinpo," South Korea's military said, but the suspected launch on had "failed".
The ministry said that it was investigating for further details.
On Saturday, a military parade was held in Pyongyang as a show of force.
North Korea marked the 105th anniversary of the birth of its founding president, Kim Il-sung, on Saturday with a huge parade in Pyongyang amid speculation that current leader Kim Jong-un could order a new nuclear test.
It came as a US aircraft carrier group steamed towards the region.
US vice President Mike Pence is also on the way area.
North Korea has already conducted five nuclear tests and a series of missile launches.
"We're prepared to respond to an all-out war with an all-out war," said Choe Ryong-hae, believed to be the country's second most powerful official.
"We are ready to hit back with nuclear attacks of our own style against any nuclear attacks," he said.
On Friday, China's Foreign Minister Wang Yi warned that "conflict could break out at any moment", and that if war happened there would be no winners.