As North Korea prepares to mark the 70th anniversary of the Kim Jong Un-led Workers' Party of Korea (WPK), there is growing speculation that the communist regime may conduct a fourth nuclear test or launch a satellite on or around October 10 as part of what is expected to be one of the country's biggest celebrations in years.

The rumors have been fueled by Pyongyang's announcement on September 15 that it restarted the long-mothballed Yongbyon reactor - capable of producing weapons-grade plutonium - and was working to improve the "quality and quantity" of weapons which it could use against the United States at "any time."

The regime added that it reserved the "legitimate right of a sovereign state" to carry out the launch of a rocket to put a satellite into orbit, a move US officials see as a potential test for ballistic missile technology.

In fact, new research suggests the North Koreans may be moving toward that goal. Analysts at the US-Korea Institute at Johns Hopkins School of Advanced International Studies recently detected new activity at North Korea's Punggye-ri nuclear test site, the location of Pyongyang's previous three nuclear detonations.

Basing their findings on recent commercial satellite photos, the latest taken on Monday, the researchers noticed an unusually large number of vehicles, camouflage netting ­- usually used to conceal activities from overhead scrutiny - and erosion control and excavation being conducted at the site.

The purpose of such activities, however, remains unclear at this point, as they could be related to anything from maintenance work to preparations for another nuclear test, said the report published on the institute's website, 38 North, on September 24.

Rocket launch 'unlikely'

At the same time, based on satellite imagery of the Sohae Satellite Launching Station (Tongchang-ri), the US analysts said that while the fourth launch of a long-range rocket was still possible, it was "unlikely" to happen on or before October 10. "Despite speculation by the international media, there are no signs at the launch pad or the Sohae facility of preparations to launch a space launch vehicle," said the experts.

And it seems that Seoul has a similar view. Jeong Joon-Hee, a spokesman for South Korea's Unification Ministry, was quoted a day later as saying that there were no signs that a North Korean rocket launch was imminent.

The statements come amid growing concerns and indications that Pyongyang is seeking to modernize its nuclear weapons program. They also follow an August report by 38 North stating that the regime had begun to refurbish a major mill located near Pyongsan - a county in the southern part of the country - that turns uranium ore into yellowcake.

North Korea fired its first rocket into space from Sohae on its west coast in December 2012

This suggests that the communist country "intends to mine and mill a significant amount of uranium that could serve as fuel for expanding its nuclear weapons stockpile," said Jeffrey Lewis, an arms control expert at the Monterey Institute of International Studies.

In April, Joel Wit, the founder of 38 North, told DW that the East Asian country was on the verge of rapidly increasing its nuclear weapons stockpile to 20, 50 or 100 bombs within five years, from an estimated 10-16 weapons at that time, adding to regional concerns.

Opacity

Pyongyang has conducted three nuclear tests since 2006 and a string of long-range rocket launches. But compared with the missile programs of other countries, North Korea has carried out only a small number of test and training launches of its indigenously produced missiles before declaring them operational, Shannon Kile, nuclear arms control and non-proliferation expert at the Stockholm International Peace Research Institute (SIPRI), told DW.

However, given the opacity of the regime's nuclear program, it is very difficult to credibly assess where the country's strategic weapon programs stand at any particular moment, so even basic questions about its nuclear weapons capabilities are shrouded in considerable uncertainty.

For example, there is no public information to verify how many operational nuclear weapons the country might possess - or indeed, whether it even has produced operational nuclear weapons as opposed to rudimentary nuclear explosive devices, says Kile, who is also head of the Nuclear Weapons Project of the SIPRI Arms Control and Non-proliferation Program.

Difficult to estimate

A statement made last October by General Curtis Scaparrotti, the commander of US forces in South Korea, about Pyongyang's ability to produce a nuclear warhead that could be mounted on a ballistic missile, made international headlines.

"They've had the right connections, and so I believe [they] have the capability to have miniaturized a device at this point, and they have the technology to potentially actually deliver what they say they have," Scaparrotti was quoted as saying.

There is no public information on how many operational nuclear weapons North Korea has

The general pointed out that while he had no evidence to back up his view, Pyongyang "probably has the background to do this." Although the general's comments seemed to be in line with a Defense Intelligence Agency report leaked in 2013, this view is not shared by all experts, either inside or outside the US intelligence community.

North Korean officials and military officers have repeatedly stated that the country's most recent nuclear test explosion, carried out in February 2013, involved a smaller and lighter "miniaturized" device with a higher explosive yield than the devices used in the two previous tests. However, these claims could not be independently confirmed.