In the short term, there seems little the world can do to stop North Korea from conducting a fifth nuclear test in the very near future.
On Monday the South Korean Defense Ministry said Washington and Seoul are monitoring an increase in activities at North Korea's Punggye-ri nuclear test site that likely indicate preparations are underway for another nuclear test.
“I cannot tell you details, but I can tell you that North Korea has the capability to conduct its fifth nuclear test anytime,” said Moon Sang-kyun, the South Korean Defense Ministry spokesman.
However, a U.S. official on Monday said the United States would respond strongly in the case of another North Korean nuclear test, Reuters reported.
U.S. Deputy Secretary of State Antony Blinken said actions by the Kim Jong Un regime in North Korea were "unacceptable" and North Korea would be digging deeper into a hole if it pursued further provocations.
“There will be additional strong response in case of another [North Korean] nuclear test,” Blinken told reporters in Tokyo, where he is meeting with senior Japanese government officials. He said Washington would consider "a number of possibilities," but said it was premature to be specific.
The Kim Jong Un government has responded defiantly after the United Nations Security Council imposed tough new international sanctions on North Korea in March for conducting its fourth nuclear test in January, followed by a long-range rocket launch in February
South Korea on alert
President Park Geun-hye on Monday called on the South Korean military to remain on high alert in case the military activity in the North leads to some sort of attack on the South.
“It is uncertain what kind of aggressive provocations North Korea will make so as to avoid isolation and strengthen the solidarity of its regime,” Park said.
North Korea’s moves to accelerate its nuclear weapons development, some analysts say, are attempts to intimidate the international community to accept it as a nuclear power and to solidify Kim’s power within the country in advance of the ruling Workers Party congress in early May.
There was also speculation that the North Koran military is under pressure to quickly conduct a successful nuclear test after a mid-range missile test on Friday ended in catastrophic failure.
North Korea is believed to have enough plutonium to make eight to 12 nuclear bombs and has a stockpile of highly enriched uranium.
South Korea’s Defense Ministry said Monday there is a good chance the next nuclear explosion will be conducted underground and that it will involve the testing of a nuclear warhead.
North Korea has claimed it has miniaturized a nuclear warhead to fit on a ballistic missile.
South Korea and the U.S. view this claim as a credible threat but say it has not been yet been demonstrated. Experts say North Korea is still years away from developing a reliable long-range nuclear missile that could reach the U.S. mainland.
In March the United Nations Security Council, which has prohibited North Korea from conducting ballistic missile and nuclear weapons tests, imposed tough new sanctions on the Kim Jong Un government.
These punitive measures, which have the potential to impose real economic pain, include suspending currency transfers and restricting North Korea’s lucrative mineral trade that had accounted for over half of the country’s $2.5 billion in exports to China alone.
Beijing’s pledged support for these international sanctions is considered crucial because 90 percent of North Korean trade flows either to or through China.
However, China seems just as concerned about maintaining stability in the region as it does about pressuring the North to give up its nuclear weapons.
It will take time to gauge the impact of the sanctions, but initial reports of lax enforcement coming from the Sino-Korean border area have raised concerns about China’s commitment to keep pressure on North Korea.
Since the sanctions were imposed, North Korea has test fired a number of short- and medium-range missiles.
The international community has condemned the repeated provocations but has imposed no additional penalties.
Kim has responded by threatening to conduct nuclear attacks against South Korea and the United States.
Following North Korea’s failed launch of a mid-range ballistic missile on Friday, China's official Xinhua news agency sharply cautioned its ally in Pyongyang, saying this “latest in a string of saber-rattling, if unchecked, will lead the country to nowhere.”
Another North Korean nuclear test in defiance of U.N. resolutions could lead to stricter enforcement of existing measures and further sanctions.
A South Korean official said Pyongyang’s next serious violation of U.N. resolutions would likely result in restrictions on the export of North Korean labor.
The Database Center for North Korean Human Rights (NKDB) estimates there are over 50,000 North Korean laborers working in China, Russia and countries around the world, and that they earn billions of dollars, most of which goes to the government in Pyongyang.
Youmi Kim in Seoul contributed to this report. Some material for this report came from Reuters.