"The two militaries staged the sixth joint aerial patrol in accordance with an annual military cooperation plan between China and Russia," the ministry said in a statement.

The statement gave no further details of the patrol, which took place over waters near Japan and the Korean peninsula.

South Korea said four Russian and four Chinese military aircraft had entered its air defence identification zone around lunchtime Tuesday, prompting Seoul's military to scramble fighter planes in response.

South Korean armed forces "identified the Chinese and Russian jets before their entry into the air identification zone", according to Seoul's Joint Chiefs of Staff (JCS).

"We deployed air force fighters to conduct tactical steps in preparation in case of an emergency," the JCS said, adding the jets did not violate Seoul's airspace.

An air defence identification zone is an area wider than a country's airspace in which it tries to control aircraft for security reasons, but the concept is not defined in any international treaty.