North Korea threatened on Sunday to conduct what it called "a new form of nuclear test", raising the level of rhetoric after members of the United Nations Security Council condemned the North's recent ballistic missile launch.

"It is absolutely intolerable that the U.N. Security Council, turning a blind eye to the U.S. madcap nuclear war exercises, 'denounced' the Korean People's Army (KPA)'s self-defensive rocket launching drills and called them a 'violation of resolutions' and a 'threat to international peace and security' and is set to take an 'appropriate step'," the North's foreign ministry said in a statement on the official KCNA news agency.

The statement said KPA drills to counter the U.S. will involve "more diversified nuclear deterrence" that will be used for hitting medium- and long-range targets "with a variety of striking power".

"We would not rule out a new form of nuclear test for bolstering up our nuclear deterrence," the North's statement said, without giving any indication of what that might entail.

After Pyongyang fired two medium-range Rodong ballistic missiles into the sea off the east coast of the Korean peninsula on Wednesday, the 15-member Security Council on Thursday condemned the launches violating U.N. resolutions.

North Korea's first firing in four years of mid-range missiles that can reach Japan followed a series of short-range rocket launches over the past two months.

In defiance of U.N. resolutions, North Korea conducted its third nuclear test in February 2013 and declared it had made progress in securing a functioning atomic arsenal.

It is widely believed the North does not have the capacity to deliver a nuclear strike on the mainland United States.