The North Korean official – commenting on the condition that his name be kept anonymous – said he doesn't know if North Korea is preparing a second nuclear test, but the North will decide whether to carry out another test "according to the development of the situation."
The North already is under limited sanctions imposed by the United States and some allies. The U.N. Security Council is considering broader measures in response to North Korea's claimed nuclear test Monday.
North Korea also has a message directly for the United States.
"If the U.S. keeps pestering us and increases pressure, we will regard it as a declaration of war and will take a series of physical corresponding measures," the North's Foreign Ministry said in a statement carried by the official Korean Central News Agency.
"We were compelled to conduct a nuclear test because of the U.S. nuclear threat and pressure of sanctions," the statement said. "We are ready for both dialogue and confrontation."
The statement was the first formal announcement from the North Korean government since KCNA reported the Monday test.
"Even though we conducted the nuclear test because of the U.S., we still remain committed to realizing the denuclearization of the Korean Peninsula through dialogue and negotiations," the ministry said.
Wednesday morning's rhetoric – ratcheting up tensions as the U.N. prepares to vote, with China now backing 'some' punitive action – came several hours after Asia was rattled by another event: a report that North Korea might have done yet another nuclear test.
The report early Wednesday sent scientists scrambling to seismic meters around the globe – but within a short time, officials in the U.S., Japan, and South Korea all said they found.
North Korea's No. 2 leader says that the decision of whether to carry out further nuclear tests depends on how the United States treats his country.
"If the United States continues to take a hostile attitude and apply pressure on us in various forms," said Kim Yong Nam, president of the Presidium of the Supreme People's Assembly, "we will have no choice but to take physical steps to deal with that."
The Bush administration has asked the U.N. Security Council to impose a partial trade embargo including strict limits on Korea's profitable weapons exports and freezing of related financial assets. All imports would be inspected too, to filter out materials that could be made into nuclear, chemical or biological weapons.
In an excerpt of a Kyodo News interview, Kim also says that North Korea is ready to return to six-party talks on its nuclear program - if existing sanctions are lifted.
South Korean President Roh Moo-hyun meanwhile says North Korea's claims of being under threat are exaggerated.
"North Korea says the reason it is pursuing nuclear (weapons) is for its security, but the security threat North Korea speaks of either does not exist in reality, or is very exaggerated" said Roh, according to Yonhap News.
South Korea also says it will enlarge its conventional arsenal - if North Korea is confirmed to have nuclear weapons.
"We will supplement (our ability) to conduct precision strikes against storage facilities and intercept delivery means, while also improving the system of having military units and individuals defend themselves," said South Korean Defense Minister Yoon Kwang-ung, speaking to the Parliament.