South Korea's unification ministry said Monday that a joint air force drill between Seoul and Washington is defensive in nature, rejecting North Korea's condemnation of the exercise.

A spokesman at North Korea's foreign ministry on Saturday denounced the exercise as a large-scale nuclear war drill against North Korea. The five-day Vigilant Ace war games kicked off Monday, days after the North fired a long-range missile.

"The air force drill is an annual joint military exercise among the allies of a defensive nature. The government will not comment on every reaction by North Korea," Baik Tae-hyun, spokesman at the Ministry of Unification, told a press briefing.

The exercise, which involves six US F-22 Raptor stealth fighter jets, came as a show of force against North Korea's nuclear and missile threats.

The North on Wednesday launched a Hwasong-15 intercontinental ballistic missile, which it claims is capable of striking the entire territory of the US, declaring that it has completed its "state nuclear force."

"The government does not accept the North's 'unilateral' claim to completing its nuclear program. We are making efforts to resolve the North's nuclear issue peacefully with the international community," Baik said.

Seoul said Friday that it does not regard North Korea as crossing a "red line" with its latest missile test due to doubts about its technical capabilities including re-entry and terminal guidance technology.

After the North's tests of two ICBMs in July, President Moon Jae-in said that North Korea would be crossing a red line if it creates a nuclear-tipped ICBM. Crossing that threshold could risk tougher actions from the US including a military one. (Yonhap)