The government lodged a protest with Beijing and Moscow over the encroachment into South Korea's air defense identification zone(KADIZ) by four Chinese and four Russian military planes without notice on Tuesday.

The defense ministry said it expressed deep regret over the incident to the defense attachés of the two countries’ embassies in Seoul on Wednesday, while requesting that they take appropriate steps to prevent a recurrence, noting that such incidents raise tensions in the region.

The foreign ministry also relayed the defense’s ministry’s regret over the incident and request to Beijing and Moscow via diplomatic channels.

As South Korea observed Memorial Day on Tuesday, the eight aircraft entered the KADIZ over southern and eastern waters in successive order between 11:52 a.m. and 1:49 p.m. before leaving the zone without violating South Korean airspace.

Upon receiving South Korea’s warning about entering the KADIZ, China told Seoul via a hotline that the planes were taking part in a regular exercise while Russia reportedly did not issue any separate statement.