North Korea said on Friday that the world would have to "wait and see" when asked for details of "a new form" of nuclear test it threatened to carry out after the United Nations Security Council condemned Pyongyang's recent ballistic missile launch.

North Korea fired two medium-range Rodong ballistic missiles into the sea on March 26. Its first firing in four years of mid-range missiles that can hit Japan followed a series of short-range rocket launches over the past two months.

Members of the Security Council on March 27 condemned the move as a violation of U.N. resolutions and that it would continue discussions on an "appropriate response."

North Korea (DPRK) reacted on Sunday with a threat to conduct what it called "a new form of nuclear test."

"The DPRK made it very clear, we will carry out a new form of nuclear test. But I recommend you to wait and see what it is," North Korea's Deputy U.N. Ambassador Ri Tong Il said on Friday during the country’s third U.N. news conference this year.

Ballistic missile launches are banned under U.N. Security Council resolutions adopted in response to North Korea's multiple nuclear tests and rocket firings. The council expanded its existing sanctions after Pyongyang's February 2013 atomic test, its third nuclear detonation since 2006.

The Security Council's sanctions on Pyongyang target the country's missile and nuclear programs and attempt to punish North Korea's leadership through a ban on the export of luxury goods to the country.

Ri accused the United States of being "hell bent on regime change" in North Korea by blaming its leaders for human rights violations. He also said Washington was blocking a bid for the denuclearization of the Korean peninsula by ignoring North Korean proposals, so it can maintain military presence in the region.

U.S. 'going around crazy'

"The U.S. is hell bent on eliminating the DPRK politically, isolating DPRK economically and annihilating the DPRK militarily," Ri told reporters. "There is a great question mark why the U.S. is hell bent on increasing the tension, ignoring the DPRK proposals, very important for peace and security."

A U.S. diplomat said that Washington had long made clear that it was open to improved relations with North Korea if Pyongyang lived up to its international obligations.

"North Korea's nuclear programs will not make the country more secure. The only way for North Korea to achieve the security and prosperity it seeks is by complying with its international obligations and commitments," the diplomat said.

Nuclear expert Jeffrey Lewis, director of the East Asia Nonproliferation Program at the Monterey Institute of International Studies in the United States, said North Korea's reference to a new form of nuclear test could mean simultaneous detonation of two or more devices as part of a program of more intense testing expected over the next few years.

Lewis said he thought it unlikely North Korean leader Kim Jong Un would move for the moment from underground to atmospheric testing - something he might do to demonstrate an ability to deploy nuclear armed missiles or artillery - for fear of inflaming Chinese public opinion.

"He's only likely to do that... if he no longer cares what Beijing thinks," Lewis said. "Still, it is useful to remember that Kim Jong Un has a number of other unpleasant provocations from which he might choose."

While North Korea has detonated several nuclear devices, analysts have expressed doubt that it currently has the technical capability to reliably mount a nuclear warhead on a missile.

Senior officials of the United States, Japan and South Korea will meet in Washington on Monday to seek ways to persuade North Korea to give up its atomic weapons program. The discussions precede a visit to Asia by Obama from April 22, which will include stops in both South Korea and Japan, where the North Korea issue will be high on the agenda.

U.N. rights investigators said in February that North Korean security chiefs and possibly Supreme Leader Kim Jong Un himself should be tried for ordering systematic torture, starvation and killings, saying the crimes were "strikingly similar" to those committed in World War Two.

"There is no human rights situation existing in the DPRK," Ri said. "The DPRK has the best social system in the world, it is based on one family as a country, fully united around our leadership, the people and the party."

"The U.S. is behaving as if it is a human rights judge while it should be subjected to the International Criminal Court more than anybody else. They made a lot of crimes," he said, citing U.S. wars in Iraq and Afghanistan.

Ri criticized military drills by the United States and South Korea, called Foal Eagle and due to end on April 18. North Korea has traditionally called for the joint exercises to be called off, seeing them as a prelude to invasion.

"The U.S. is now going around crazy with these joint military drills without caring about peace and security on the Korean peninsula," Ri said.

The annual drills have been conducted for decades without a major incident. The United States and South Korea stress that the exercises are purely defensive and aimed at testing readiness against any possible North Korean aggression.