'N.Korean military plane activities on unusual rise'

North Korea has shown an "unusual increase" in inspecting its artillery's readiness and carrying out air force flight operations, heightening tensions in the region, South Korean Defence Minister Jeong Kyeong-doo said on Friday.

"North Korea has been heightening military tensions through an unusual increase in the inspection activities for its combat readiness posture, mostly of its artillery, and in its air force planes' flight operations," Yonhap News Agency quoted Jeong as saying.

Along with smaller-scale artillery firing drills, the communist country has conducted five major weapons tests this year.

The latest one took place last week, during which the North fired what appeared to be surface-to-ship cruise missiles off its east coast.

On the same day, the North also flew Sukhoi-variant fighter jets and MiG-type planes above the eastern coastal city of Wonsan, and fired multiple air-to-ground missiles into the East Sea.

A Joint Chiefs of Staff officer earlier said there has been an increase in North Korea's surveillance activities in skies near its demarcation line with China over the Yellow Sea, adding that some maritime and air spaces over the body of waters have not been clearly declared either by Pyongyang or Beijing.