North Korea’s plan to conduct a third nuclear test is “needlessly provocative” and will only increase its isolation, the White House said Thursday.

Defense Secretary Leon Panetta said he has seen no outward sign that North Korea will follow through soon on its plan to conduct a test ― following its underground atomic explosions in 2006 and 2009. But the U.S. is fully prepared against any kind of provocation, he said.

Washington slapped economic sanctions on two North Korean bank officials and a Hong Kong trading company that it accused of supporting Pyongyang’s proliferation of weapons of mass destruction.

China’s state-run media said on Friday Beijing will decrease aid to Pyongyang if it goes ahead with a planned nuclear test.

On Thursday North Korea’s National Defense Commission said a nuclear test was part of “upcoming” action directed against the U.S., but did not say exactly when or where it would take place.

The commission, led by leader Kim Jong-un, also made clear that its long-range rockets were designed to carry warheads aimed at striking the United States. The North has previously said its launches are for a peaceful space program.

Pyongyang’s statement came two days after the U.N. Security Council condemned its December launch of a satellite atop a long-range rocket for violating a ban on ballistic missile activity. The council, with the support of the North’s only major ally, China, also tightened sanctions.

“North Korea’s statement is needlessly provocative and a test would be a significant violation of United Nations Security Council resolutions,” White House spokesman Carney told reporters. “Further provocation would only increase Pyongyang’s isolation, and its continued focus on its nuclear and missile program is doing nothing to help the North Korean people.”

Carney said the council decision to tighten sanctions would impede the growth of weapons of mass destruction programs in North Korea. He said the U.S. would be taking additional steps. The government later designated as “trade” several entities said to be involved in missile development.

Carney noted the council’s warning to take further action in the event of a further launch or nuclear test.

“We judge North Korea by its actions, and provocations like these are significant violations and we act accordingly,” Carney said.

Defense Secretary Panetta said the United States is “very concerned” about North Korea’s threat but is prepared to deal with any kind of provocation from Pyongyang.

Panetta, speaking at a Pentagon news conference, said North Korea’s actions would violate U.N. Security Council resolutions, distance Pyongyang from the international community and “do nothing, nothing other than jeopardize the hope for peace.”

“We are very concerned with North Korea’s continuing provocative behavior,” Panetta said. “We are fully prepared ... to deal with any kind of provocation from the North Koreans. But I hope in the end that they determine that it is better to make a choice to become part of the international family.”

The U.S. Treasury Department levied sanctions against a Hong Kong-based trading company and two officials of a North Korean bank.

The two men worked for North Korea’s Tanchon Commercial Bank. The company, Leader (Hong Kong) International Trading Ltd, was separately blacklisted by the United Nations on Wednesday.

Leader is an agent for KOMID, a North Korean mining and trading company that was sanctioned in 2009 and is the country’s main arms dealer, the United Nations said.

“Our actions today target two North Korean entities, Tanchon Commercial Bank and KOMID, that are part of the web of banks, front companies and government agencies that support North Korea’s continued proliferation activities,” said David Cohen, U.S. Treasury undersecretary for terrorism and financial intelligence.

The action bans contact between any U.S. citizen and Ra Kyong-su, TCB representative to Beijing, and Kim Kwang-il, TCB deputy representative to Beijing, and freezes their assets. It also freezes the assets of, and bans contact with, Leader.

“By continuing to expose these entities, and the individuals who assist them, we degrade North Korea’s ability to use the international financial system for its illicit purpose,” Cohen said in a statement.

China, the North’s leading energy supplier and trade partner and one of the few nations able to influence Pyongyang’s behavior, issued an unusually frank warning Friday.

“If North Korea engages in further nuclear tests, China will not hesitate to reduce its assistance to North Korea,” the Global Times, which is close to the ruling Communist Party, said in an editorial.

“China hopes for a stable peninsula, but it’s not the end of the world if there’s trouble there,” it added.

“We should have a pragmatic attitude to deal with the problems and pursue the optimal ratio between our investment of resources and strategic gains.”

The editorial also expressed discontent at North Korean criticism of Beijing for backing a U.N. Security Council resolution this week.

(From news reports)