North Korea on Tuesday staged a live-artillery exercise in waters near the South, and the regime issued a fresh nuclear warning, news reports said.
Roughly 50 munitions were fired from two coastal military facilities in the afternoon, the Yonhap News Agency reported. South Korea was notified ahead of time about the maritime exercise and did not return fire as no North Korean shell crossed into its territory.
Meanwhile, a powerful North Korean military body on Monday threatened to do "more than nuclear tests" in response to recent international warnings on the matter.
"The world is making all the guesses and conjectures that our new nuclear test and the rocket launch will develop into a boosted fission weapon or a new generation of intercontinental ballistic missiles," the North Korean National Defense Commission said in a statement quoted by the Choson Ilbo newspaper.
"If you ask us to tell the truth, we will not deny that we are capable of doing more than these speculations," the defense commission said.
The United States and South Korea are keeping a close eye via satellites on the North's Punggye-ri nuclear test site, where personnel appear to be in the thick of preparations for an expected fourth underground atomic trial. U.S. President Obama and South Korean President Park Geun-hye on Friday warned that Pyongyang could expect more sanctions and an end to any hope of reviving a moribund aid-for-denuclearization process if it proceeds with the test.
In related news, the South Korean government on Monday authorized a plan to boost domestic missile defenses by upgrading existing interceptors and purchasing more-capable systems from the United States, the Korea Times reported.
Under the approved plan, the South would acquire as many as 100 Patriot Advanced Capability 3 missiles between 2016 and 2020 and would seek to buy upgrades for its 48 PAC-2 systems through a competitive bid process, the Korea Herald reported.
The new interceptors and missile upgrades will be used to boost the effectiveness of the country's Korea Air and Missile Defense framework, which is designed to counter lower-altitude ballistic missiles fired by North Korea.