Pak Myong-guk, an official at the North's embassy in Australia who described his title as minister, echoed the wording of Tuesday official announcement from Pyongyang that the North was compelled by threats of nuclear war and US economic sanctions to conduct a nuclear test at some time in the future.
The statement from Pyongyang gave no precise date when a test might occur.
Asked about US Secretary of State Condoleezza Rice's comment such a test would be a provocative act, Pak on Wednesday told The Associated Press: "It is not provocative, it is just the corresponding measure for defence, for us to defend ourselves. It is the really essential process for nuclear deterrent."
Responding to the announcement, South Korea urged North Korea on Wednesday to renounce its nuclear test plan and return to international disarmament talks, saying Seoul won't tolerate the North's possession of nuclear weapons.
"We express grave concern and regret," Choo Kyu-ho, the country's foreign ministry spokesman, said. "We urge North Korea to immediately scrap the nuclear test plan. In addition, the North should return to six-party talks unconditionally without taking any further steps aggravating the situation."
"If North Korea pushes ahead with a nuclear test, North Korea should take full responsibility for all consequences." He didn't elaborate.
The South's announcement came after the country held an emergency meeting of security ministers earlier in the day.
Japan for talks
For his part, Shinzo Abe, Japan's new prime minister, is to discuss the issue with the leaders of China and South Korea in summits to be held next week, reports said on Wednesday.
Pyongyang's pledge to test a nuclear weapon will top the agenda for Abe's fence-mending summits with Tokyo's neighbors, the Yomiuri Shimbun reported, citing unnamed foreign ministry sources.
"I plan to discuss the regional situation including North Korea," Abe said late on Tuesday, when asked about the expected summits in Beijing and Seoul, the Yomiuri and other major local media reported.
Japan was to officially announce on Wednesday that Abe would visit China and South Korea on Sunday and Monday - a trip initially planned to help soothe strained ties with the Asian neighbours.
On his part, Australia's foreign minister said on Wednesday he wanted a meeting with the North Korean ambassador to Australia over the Asian country's "deeply offensive" nuclear test plan.
Alexander Downer said that he would seek a meeting with Ambassador Chon Jae Hong on Wednesday to discuss the implications of North Korea's announcement that it plans to conduct a nuclear test.
Australia, a close security ally of the US, is one of the few Western countries to have limited official ties with North Korea.
"It's highly provocative. It's deeply offensive to the whole of the region," Downer told the Australian Broadcasting Corp late on Tuesday. "So we will obviously very strongly express our views, including directly to the North Korean ambassador."