North Korea said Tuesday its military would launch its first-ever reconnaissance satellite in June to monitor in real time "hostile military activities" led by the US, amid a doubling down on joint military drills by South Korea and the US.

In a statement by the North’s state media Korean Central News Agency, Ri Pyong-chol, vice chairman of the Central Military Commission of the ruling Workers’ Party of Korea, said “careless military movements by Washington and Seoul” have prompted the need for such a launch, which he described as nothing more than an act of self-defense.

South Korea and the US, its biggest ally, last week conducted what they said were their largest-ever joint live-fire exercises -- part of the Yoon administration’s strategy to denuclearize the North, which involves projecting strength.

The conservative leader, who took office last year, resumed the joint military drills, giving priority to containment amid stalled dialogue.

North Korea is banned by United Nations resolutions from firing off any projectiles using ballistic missile technology, which would include the planned spy satellite. Pyongyang did not disclose the exact launch date but has notified Japan of a launch between May 31 and June 11.

Japan publicly reiterated its policy that it would shoot down any projectiles threatening its territory, with Japan’s Chief Cabinet Secretary Hirokazu Matsuno saying it asked Pyongyang to hold off on the launch. Japanese Prime Minister Fumio Kishida said he would closely work with his South Korean and US counterparts to deal with North Korea’s latest show of aggression.

A deputy spokesperson for Seoul’s Defense Ministry said at a regular briefing that South Korean and US intelligence authorities are closely monitoring developments, without elaborating whether they would also shoot down any projectiles fired by North Korea. The Foreign Ministry in Seoul released a statement, saying the launch, which “is clearly illegal,” will be met with a “stern response.”

The Tuesday announcement comes at a time when South Korea kicked off a four-day global gathering of senior security officials from over 70 countries taking part in the Proliferation Security Initiative -- an ad hoc alliance of states launched by the US in 2003 to stop shipments of weapons of mass destruction. It was the first time such a meeting took place in Asia.

Held every five years, the meeting involves face-to-face discussions as well as maritime exercises to bolster global readiness on containing WMD. The drills will take place in the international waters southeast of Jeju Island. South Korea, the US and Japan -- the three partners working on disarming the North -- plus Australia, Canada and Singapore will participate in the drills.

But officials in Seoul said Wednesday’s drills would be scaled down because of bad weather. While the exercises are not meant to prepare for confrontations with specific countries, officials in Seoul believe they will serve as a check on Pyongyang, as the isolated regime continues to defy international sanctions in place for its nuclear and missile programs.

“The PSI meeting was an opportunity to reaffirm the international community’s commitment to nonproliferation when the task has become ever more important in the face of growing nuclear threats from North Korea,” the Foreign Ministry in Seoul said in a statement after the gathering.