This year alone has seen at least eight signs of either nuclear tests or delivery methods. Some analysts believe the regime may be gearing up for another nuclear test
-- its fifth.
Each test offers an opportunity to learn from mistakes either in launch capability or the nuclear program.
Joel Wit, a senior fellow at the U.S.-Korea Institute at the Johns Hopkins School of Advanced International Studies, says the regime is pursuing technological developments, both on the nuclear and delivery systems sides.
In terms of developing the nuclear technology, each test gives Pyongyang's nuclear scientists an opportunity to gain invaluable data that is helping them miniaturize the devices, reduce the amount of nuclear material needed for each bomb, and increase their yield.
They are also developing missiles that can reach targets from South Korea to the U.S., and developing more advanced technology, such as solid fuel rocket engines, larger liquid fuel rockets and submarine-based launches.
The aim, he says, is "first to grow size of nuclear stockpile, and increase the type of delivery systems to ensure second strike capacity."
How much fissile material does Pyongyang have?
Analysts are asking how much weapons-grade plutonium North Korea still possesses, given the rate at which it has been testing its weapons.
"North Korea may have used up to half of the plutonium they reprocessed in 2003, but no one can be sure without knowing how much plutonium was used for each test," says Scott Snyder, senior fellow for Korea studies and director of the program on U.S.-Korea policy at the Council on Foreign Relations (CFR).
"There is great uncertainty about the rate of new production of fissile material since 2009, but it is possible and even likely that they have replaced the amounts that they have used."
What are its delivery capabilities?
North Korea's missile development program began in the 1960s, and by 1971 the country had signed an agreement with China to develop and produce ballistic missiles. It has also partnered with Iran on missile development.
By 1984, according to
the Nuclear Threat Initiative, it had developed the Hwasong-5, a homegrown version of the Scud missile.
Since then it has developed or is developing as many as eight delivery vehicles. The submarine-based Bukgeukseong-1, a Polaris-variant, is the latest in development. North Korea is believed to have fired one off the east coast of the Korean peninsula
Its intermediate-range Nodong (also called Rodong) was developed in the late 1980s and successfully test-launched in 1993.
North Korea's arsenal has weapons which can potentially reach the continental United States. The three-stage, liquid fueled ballistic/space launch missile Kwangmyongsong, also known as the Unha-3 mod or 2 Taepodong-3, has a range of 12,000 km (7,456 miles).
In February, North Korea said it had launched a satellite into space
, triggering international condemnation and a strong reaction from an emergency meeting of the U.N. Security Council.
North Korea says the launch is for scientific and "peaceful purposes," but it is widely viewed by other nations as a front to test a ballistic missile, especially coming on the heels of North Korea's purported hydrogen bomb test a month earlier.
In March, Pyongyang announced
it had miniaturized its nuclear warheads so they could be fitted to ballistic missiles.