The United Nations' air navigation regulator, International Civil Aviation Organization, has issued a warning to North Korea for its recent ballistic missile launches that came without the necessary advance notifications, the foreign ministry said Thursday.

"The ICAO has sent a letter of warning to North Korea under the name of the chairman of its board," Cho June-hyuck, spokesman at the Ministry of Foreign Affairs, said in a regular briefing.

The warning followed North Korea's recent series of ballistic missile launches including the test-firing of three mid-range missiles on Monday.

Under international treaties, countries planning a rocket launch are required to give advance notification to relevant UN regulators, including ICAO, in order to warn planes and ships to stay clear of the areas that could be affected by the flight.

North Korea failed to follow through on the required procedures before its latest launches. That prompted Seoul to prod ICAO and the International Maritime Organization last month for countermeasures.

"Our government has been in close cooperation with the ICAO and IMO over North Korea's unannounced missile launches," Cho said.

"Currently, the government is also in collaboration with the IMO for related countermeasures."  (Yonhap)