John Bacon

USA TODAY

North Korea is preparing another mid-range missile test and could also conduct a fifth nuclear test, South Korean officials said Tuesday.

The reports come three days after the North claimed it successfully fired a ballistic missile from a submarine for the first time.

The latest development adds to a string of troubling reports of nuclear weapons and ballistic missile tests that have raised tensions on the Korean Peninsula and led to a tightening of international sanctions. Pyongyang has blamed South Korea and the West for the tensions, vehemently objecting to joint U.S.-South Korean military exercises and repeatedly issuing nuclear strike threats against Seoul and Washington.

There is a chance that tensions could ease somewhat in coming weeks. James Person, who coordinates the Center for Korean History and Public Policy at the Washington-based Wilson Center, said much of the North's saber rattling could be an effort by leader Kim Jong Un to appear strong ahead of the Korean Workers Party Congress expected to take place in early May.

"These provocative acts have been largely timed to project power to the domestic audience," Person told USA TODAY. He said the completion of the U.S.-South Korean exercises also could calm Pyongyang.

President Obama, in an interview with CBS News, called relations with North Korea a "massive challenge" and described Kim as "irresponsible." He said the United States is positioning its missile defense system to block any military threat from Pyongyang.

"We could, obviously, destroy North Korea with our arsenals," Obama said. "But aside from the humanitarian costs of that, they are right next door to our vital ally, Republic of Korea."

On Tuesday, South Korea's Yonhap News Agency, citing military and government sources, said "signs have been detected" that North Korea will soon try to launch another Musudan missile from a land-based site. A Musudan, or BM-25, is believed to be capable of traveling 2,500 miles, posing a threat to South Korea, Japan and the U.S. territory of Guam.

North Korea claims success firing missile from sub

On April 15, North Korea made a "fiery, catastrophic attempt" to launch a mid-range missile that was detected and tracked by the U.S. Strategic Command systems, the Pentagon said. South Korea's Joint Chiefs of Staff also said that North Korea had fired one of two mobile Musudan missiles from a launch site in the eastern port city of Wonsan.

That launch apparently was timed to coincide with the 104th anniversary of the birthday of the country's late founder Kim Il Sung.

"The remaining missile appears to be standing by for launch," Yonhap said Tuesday.

Also Tuesday, South Korean President Park Geun Hye said North Korea is fully prepared to conduct a fifth nuclear test, the Associated Press reported. And the Institute for Science and International Security issued a report this week indicating that no vehicle or personnel movement has been detected at the North Korean test site in recent days — a sign that test preparations may be completed.

Pyongyang's activities have put pressure on the South Korean military, now facing calls from the ruling Saenuri Party to develop a nuclear-powered submarine as a countermeasure to North Korea's submarine-based ballistic missiles, the Korea Times reports. Concerns rose after Saturday's test-launch of a missile from a North Korean submarine.

Person stressed that Pyongyang's goal is preservation of the regime. Still, he said a longtime North Korean policy emphasizing military strength and heavy industry was tweaked in recent years to stress nuclear buildup and improve living conditions.

"They went from guns and steel to nukes and butter," Person said. "They have the nukes, we can hope they decide to start concentrating on the butter."