The United States warned North Korea on Tuesday not to make a "mistake" deepening its isolation after the communist nation has strongly hinted at the possibility of conducting a nuclear or missile test.

"It would be a mistake for North Korea to once again embark on the kind of threatening behavior and provocations that led to international sanctions in the first place," Assistant Secretary of State Daniel Russel told reporters after a speech at the Woodrow Wilson International Center for Scholars.

"For North Korea to conduct a missile or a nuclear test would represent a setback in its hopes to grow its economy and to end its isolation. It would deal a setback to the world's hopes for successful negotiations," the official said.

North Korea has ratcheted up tensions this week with apparent threats to conduct missile or nuclear tests.

On Monday, the North strongly hinted at the possibility of conducting a long-range rocket launch. Pyongyang also said Tuesday that the uranium enrichment plant and the plutonium-producing reactor at its Yongbyon nuclear complex has started normal operation.

It also said it's ready to cope with the U.S. hostile policy toward it "with nuclear weapons any time."

White House press secretary Josh Earnest urged the North to refrain from "irresponsible provocation."

"We will not accept North Korea as a nuclear state, and that's why we urge North Korea to refrain from actions and rhetoric that threaten regional peace and security and focus instead on fulfilling its international obligations and commitments," he said.

Pentagon press secretary Peter Cook said the U.S. is closely monitoring the situation.

"We are in close contact with the Republic of Korea and our allies there remain committed to the defense of the Republic of Korea," he said. "we call on Pyongyang to refrain from actions and rhetoric that threaten regional peace and stability and security in the area."

Russel urged Pyongyang to stick to its responsibilities under U.N. Security Council resolutions.

"North Korea's committed to denuclearization. North Korea is prohibited from conducting any ballistic missile activities," he said. "Now North Korea has been down on this road before and what does it get? It cannot get, will not get the security or the benefits of the dynamism of Northeast Asia by violating international law."

Russel also said Pyongyang can get what it wants, such as economic growth, security and respect, if it makes the right decisions and the right path.

"President (Barack) Obama, President Park (Geun-hye) have extended hands to North Korea. North Korea should unclench its fist and we hope that North Korea would not follow through on provocative actions that would serve as a setback to regional security," he said.

The way out for North Korea is "bona-fide negotiations to engineer meaningful and irreversible steps toward denuclearization," he said.

"Our position and our efforts have been aimed at trying to engineer resumption of negotiations on the nuclear issue for the purpose of fulfilling the commitment that all six nations made in 2005, which is to completely and verifiably denuclearize the Korean Peninsula," Russel said.

"That is the only path that is available to North Korea to deal with its economic problems and to achieve realistic security. The net effect of North Korea's decisions and pursuit of nuclear weapons or missile capability is frankly only to deter prosperity," he said.

The official said that denuclearization of the Korean Peninsula was a focus of Park's summit with Chinese President Xi Jinping earlier this month, and the goal will also be a focus of Obama's talks with Xi, set for next week, and the talks with Park, set for next month. (Yonhap)