North Korean leader Kim Jong Un oversaw the test of hypersonic missiles a day after the U.S. seized Venezuelan leader Nicholas Maduro in an act that Pyongyang denounced as a “rogue and brutal” violation of international laws.

The missiles were fired on Sunday to verify the weapon system’s sustainability and effectiveness, official Korean Central News Agency reported Monday. The projectiles, launched from the Pyongyang area northeastward, hit targets 620 miles away, it said.

The missile launches also came as South Korea’s President Lee Jae Myung was prepared to meet with Chinese President Xi Jinping in Beijing later Monday.

South Korea’s military earlier said North Korea launched suspected ballistic missiles on Sunday morning that flew around 900 km.

“Important achievements have been recently made in putting our nuclear forces on a practical basis and preparing them for an actual war,” Kim was quoted as saying by the KCNA. “We must continuously upgrade the military means, especially offensive weapon systems.”

The U.S., China, North Korea and others are in a race to develop hypersonic weapons with maneuverable gliders that are too quick and agile for traditional missile defense systems to detect in a timely fashion. It remains to be seen if North Korea has actually developed a functional hypersonic glide vehicle.

Kim did not directly mention the U.S. operations in Caracas over the weekend to remove Maduro from office, but said “the recent geopolitical crisis and complicated international events” show why it is necessary to develop the country’s nuclear war deterrent.

North Korea’s Foreign Ministry on Sunday strongly denounced the U.S. raid as “the most serious form of encroachment of sovereignty and as a wanton violation of the U.N. Charter and international laws.”

Lim Eul-chul, professor at the Institute for Far Eastern Studies at Kyungnam University, said the capture of Maduro “will cement Kim’s belief that abandoning nuclear weapons is tantamount to suicide.”

“This will likely make denuclearization efforts on the Korean Peninsula even more difficult, increase the unpredictability of North Korean behavior, and further justify and accelerate the advancement of nuclear capabilities,” Lim said.

North Korea’s Foreign Ministry said in a statement carried by KCNA that the actions by Washington confirmed “once again the rogue and brutal nature of the U.S.,” which the international community has so frequently witnessed.

As the first sitting South Korean president to visit China since 2019, Lee is expected to seek Beijing’s help in tempering regional tensions, including with regards to North Korea.