North Korea has continued to install land mines and barriers within the Demilitarized Zone (DMZ) separating the two Koreas despite recent heavy downpours and mine explosions, Seoul's defense ministry said Thursday.North Korea has deployed large numbers of troops in front-line areas to plant mines and erect walls presumed to be anti-tank barriers since April, according to South Korean military officials.Such activities within the DMZ have continued to be detected even after mine explosions and as seasonal rains recently battered the North, the ministry said in a policy report to the National Assembly.Last month, the ministry said North Korea suffered multiple troop casualties inside the DMZ due to mine explosions and heat exhaustion.The ministry also said North Korea is preparing for an additional military spy satellite launch following its failed attempt in May, when its satellite-carrying rocket exploded soon after liftoff.Pyongyang has vowed to launch three spy satellites into orbit this year aft er successfully launching the Malligyong-1 reconnaissance satellite last year.Meanwhile, the report said North Korea has launched 37 ballistic missiles on eight occasions this year, while firing 11 cruise missiles on six instances.To bolster defense readiness, South Korea has expanded combined exercises with the United States, it said, staging 10 large-scale combined drills in the first half of this year -- double the figure over the same period the previous year."North Korea is continuously advancing its nuclear and missile capabilities despite opposition from the international community," Defense Minister Shin Won-sik said in a parliamentary session of the National Defense Committee."(It) is seriously threatening peace and stability not only on the Korean Peninsula and in the Indo-Pacific region but also Europe and the entire world."Source : Yonhap News Agency