A North Korean missile has detonated soon after launch, South Korean and US military officials have said, a day after Pyongyang warned the US amid rising tension in the region.
The US said a ballistic missile exploded within seconds of launch.
Hours earlier, North Korea paraded what appeared to be long-range ballistic missiles at a major military display.
It has already conducted five nuclear tests and a series of missile launches in contravention of UN resolutions.
The latest development came as US Vice-President Mike Pence arrived in the South Korean capital, Seoul, where he was expected to discuss the best way to deal with North Korea's missile and nuclear programmes.
Mr Pence, beginning a long-planned 10-day Asia trip, his first official visit to the region, addressed US soldiers at an Easter service, telling them that the commitment to South Korea had "never been stronger".
The South Korean defence ministry said that "North Korea attempted to test an unidentified type of missile from [its eastern port of] Sinpo". It added that the launch on Sunday had "failed".
The US Pacific Command later confirmed the failed test, adding that it had detected and tracked what it believed to be a North Korean ballistic missile.
On Saturday, North Korea marked the 105th anniversary of the birth of its founding president, Kim Il-sung, with a huge military parade in Pyongyang amid speculation that current leader Kim Jong-un could order a new nuclear test.
The event appeared to include new intercontinental and submarine-launched ballistic missiles.
"North Korea showing a variety of offensive missiles at yesterday's military parade and daring to fire a ballistic missile today is a show of force that threatens the whole world," South Korea's foreign ministry said in a statement.
Adding to the tension in the Korean peninsula, a US aircraft carrier group is steaming towards the region.
Washington has stepped up pressure on the isolated North, with President Donald Trump saying that the US is ready to act alone to deal with the nuclear threat.
At the parade on Saturday, North Korean military official Choe Ryong-hae, who is believed to be the country's second most powerful official, said that his country was "prepared to respond to an all-out war with an all-out war".
"We are ready to hit back with nuclear attacks of our own style against any nuclear attacks," he said.
North Korea has suffered test failures in the past but they have not deterred its development programme. Pyongyang resident Rim Chung-ryol told Reuters: "If the news is true, failure is the mother of success. We will make more efforts to make even more powerful weapons in the future."
North Korea's aim is to be able to put a nuclear warhead on an ICBM that can reach targets around the world.
Pyongyang has claimed to have miniaturised nuclear warheads for use on missiles, though experts have cast doubt on that given the lack of evidence.
The state is banned from any missile or nuclear tests by the UN, though it has repeatedly broken those sanctions.
Earlier this month, North Korea test-fired a medium-range ballistic missile from Sinpo into the Sea of Japan.
The launch took place on the eve of a visit by China's President Xi Jinping to the US to meet Mr Trump.
The two later discussed how to rein in North Korea's nuclear and missile programmes.
On Friday, China's Foreign Minister Wang Yi warned that the situation in the region was escalating, adding that "conflict could break out at any moment". Mr Wang said that if war occurred, there could be no winner.