"The military detected an unidentified projectile launched from the Pyongyang area on Tuesday," the military said in a statement without giving further details.

"Detailed specifications are being analysed by South Korean and US intelligence authorities," it added.

The launch follows Seoul's expression of regret on Monday over civilian drone incursions into the North in January, with President Lee Jae Myung calling it "irresponsible" and noting that government officials had been involved in the operation.

Following his comments, the powerful sister of North Korean leader Kim Jong Un said Lee's regret was "wise behaviour".

"Our government appreciated it as very fortunate and wise behaviour for its own sake," Kim Yo Jong said on Monday.

But on Tuesday, a senior North Korean foreign ministry official described the South as "the enemy state most hostile to the DPRK", using the initials of the North's official name, reiterating a label used by leader Kim previously.

Referring to South Korean media reports that cast a positive light on Kim Yo Jong's comments about Lee, the official said such a stance was "nonsense".

"Regarding the rapid response from our government as an 'exceptional friendly response'... this will also be recorded as world-startling fools' 'hope-filled dream reading'", Jang Kum-chol, first vice?minister of Pyongyang's foreign ministry, said in an English statement carried by the official Korean Central News Agency.