A trio of Nobel laureates will take part in a "humanitarian" visit to North Korea later this month, even as suspicions grow that Pyongyang is preparing to carry out a fifth nuclear test.

The Vienna-based International Peace Foundation, which is organising the trip, said Monday it was an exercise in "silent diplomacy" that would focus on such topics as economic policy and medical development.

The three laureates from Norway, Britain and Israel, who won their Nobels for economics, medicine and chemistry, will give speeches and hold seminars with students at some of the North's elite schools, including Kim Il-Sung University.

"The events will not engage in rhetoric by making political statements," the foundation said in a press release.

"Listening to and engaging with the young generation of (North Korea) may be a gateway to establish a dialogue which could contribute to a wider understanding beyond politics and power play," added its founding chairman, Uwe Morawetz, who has visited the North six times over the past two years to prepare the visit.

The trip is likely to be criticised in some quarters at a time when the focus of the international community is on tightening North Korea's diplomatic and economic isolation.

The April 29-May 6 dates mean the visit might also coincide with a fresh North Korean nuclear test.

South Korean President Park Geun-Hye confirmed Monday that increased activity had been detected at the North's nuclear test site at Punggye-ri, suggesting an underground detonation could be imminent.

Numerous analysts have predicted Pyongyang may carry out a fifth test just before a rare ruling party congress next month, at which leader Kim Jong-Un is expected to take credit for pushing the country's nuclear weapons programme to new heights.

No formal date has been set for the congress, but South Korea's intelligence agency says it will likely be held May 7.

North Korea conducted its fourth nuclear test in January, triggering the most extensive UN sanctions to date aimed at cutting funding sources for its nuclear development.

The Nobel laureates will hold a press conference in Beijing after returning from their visit.

S. Korea's Park says North preparing nuclear test
Seoul (AFP) April 18, 2016 - South Korean President Park Geun-Hye on Monday said North Korea appeared to be readying for a fifth nuclear test in defiance of tightened UN sanctions imposed after its last test in January.

"Signs that it is preparing a fifth nuclear test have recently been detected," Park told a cabinet meeting.

Her remarks followed South Korean media reports in which unnamed government and intelligence officials spoke of a spike in activity at the North's Punggye-ri nuclear test site.

A fresh test would see Pyongyang doubling down in the face of tough sanctions adopted by the UN Security Council, and would throw down a gauntlet to the international community as it struggles to find new ways to curb the North's nuclear ambitions.

North Korea is gearing up for a rare and much-hyped ruling party congress early next month, at which leader Kim Jong-Un is expected to take credit for pushing the country's nuclear weapons programme to new heights.

Numerous analysts have suggested the regime might carry out a fifth nuclear test as a display of defiance and strength just before the congress opens.

"It is uncertain what kind of unexpected provocations it would stage," Park said at the cabinet meeting.

The South Korean Defence Ministry said it was alert to the likelihood of a fifth test.

"Given current activities, we believe that there is a possibility that the North may stage an underground nuclear test, and are monitoring the situation accordingly," ministry spokesman Moon Sang-Gyun told reporters.

South Korea's vice foreign minister will discuss the North Korean threat during trilateral talks this week with his US and Japanese counterparts in Seoul.

Tension has been high on the divided Korean peninsula since the January test and a rocket launch a month later that was widely seen as a disguised ballistic missile test.

The UN Security Council responded by imposing its strongest sanctions to date over the North's nuclear weapons programme.

Pyongyang has responded defiantly, staging a series of short- and mid-range missile tests and claiming a series of significant technical breakthroughs in its nuclear strike capability.

It claimed it had miniaturised a nuclear warhead to fit on a missile and successfully tested an engine designed for an inter-continental ballistic missile that could reach the mainland US.

While some experts say the claims are exaggerated, most acknowledge that the North's nuclear and ballistic missile programmes have made significant strides.