A spokesperson from the Foreign Ministry said South Korea was introducing "F-35A" stealth fighters - "a cutting-edge lethal equipment" - from the US, after the just-ended joint military exercises, Xinhua on Thursday quoted a statement by Korean Central News Agency.
The act "is a grave provocation that has openly denied the joint declarations and the military agreement" between the two sides on the Korean Peninsula, he said.
The spokesperson said that the hostile military moves, including the US-South Korea joint military exercises and the build-up of armed forces in South Korea, are reducing the dynamics of dialogue for building lasting and durable peace on the Korean Peninsula, and compel North Korea to "weigh a realistic way of turning our attention more to strengthening the physical deterrence".
North Korea fired two unidentified projectiles into the sea off its east coast on August 16 shortly after it denounced the US-South Korea military drills and declared that inter-Korean talks were over.
However, the spokesperson said his country remains unchanged in its position to "resolve all issues in a peaceful manner through dialogue and negotiation".
Denuclearisation talks between North Korea and the US have been stalled despite a commitment made to revive them at a meeting on June 30 between North Korean top leader Kim Jong-un and US President Donald Trump.
( With inputs from IANS )