South Korea's defense chief ordered the military to tighten vigilance against a possible North Korean provocation on Monday, one day after its latest missile test, the defense ministry said.

Defense Minister Han Min-koo visited the Aviation Operations Command in Icheon, 80 kilometers south of Seoul, to inspect the ongoing deployment of AH-64D Apache heavy attack helicopters, the ministry said in a statement.

As part of a scheduled rotational deployment, the 24 AH-64D Apache choppers will gradually replace the 30 OH-58D Kiowa Warrior observation and light attack choppers this month. 

Han instructed airmen to maintain the "Fight Tonight" posture as the command will play a key role in the Korea Massive Punishment & Retaliation plan.

The KMPR directly targets the North's military leadership with the aim of neutralizing key figures and infrastructure if there are clear signs of the imminent use of nuclear weapons.

This year, Seoul plans to launch a special unit tasked with incapacitating North Korea's wartime leadership as it strives to better counter Pyongyang's evolving nuclear and missile threats.

On Sunday, Pyongyang test-fired a new type of intermediate-range ballistic missile in what could be part of efforts to develop an intercontinental ballistic missile capable of reaching the U.S. mainland. (Yonhap)