North Korea on Saturday test-fired two short-range ballistic missiles, its neighbours said, the fourth round this week of weapons launches that prompted quick, strong condemnation from its rivals.

In an unusually strong rebuke of North Korea's weapons programs, South Korean President Yoon Suk Yeol said North Korea's “obsession” with nuclear weapons is deepening the suffering of its own people, and warned of an “overwhelming response” from South Korean and US militaries should such weapons be used.

“North Korea hasn't abandoned its obsession with nukes and missiles despite the persistent international objection in the past 30 years,” Yoon said during an Armed Forces Day ceremony.

“The development of nuclear weapons will plunge the lives of North Korean people in further pains.”

“If North Korea attempts to use nukes, it'll face a resolute, overwhelming response by the South Korea-US alliance and our military,” Yoon said.

Yoon's comments could enrage North Korean leader Kim Jong Un, who has alleged that Yoon's government was led by “confrontation maniacs” and “gangsters”.

Kim has already rebuffed Yoon's offers of massive aid and support plans in return for denuclearisation.

The North's testing spree this week is seen as a response to recent naval drills between South Korea and the US and their other training that involved Japan.

North Korea views such military exercises by the allies as an invasion rehearsal and argues they reveal US and South Korean “double standards” because they brand the North's weapons tests as provocation.

On Saturday, South Korea, Japanese and US militaries said they detected the two North Korean missile launches. South Korea said the liftoffs occurred from North Korea's capital region.