Nuclear-armed North Korea fired an "unidentified projectile" Wednesday that appeared to fail immediately after launch, the South Korean military said, amid warnings from the U.S. and its allies of an imminent test of long-range missile technology.

South Korea's Joint Chiefs of Staff said the launch attempt happened around 9:30 a.m. at Sunan Airport outside Pyongyang, the same site as the country's two most recent missile tests.

"At this point, our assessment is that the projectile launch appears to have been botched, as it failed to reach a certain altitude in its early boost phase," a South Korean military official told the Yonhap news agency on condition of anonymity.