A senior U.S. government official said Tuesday North Korea is still obliged to follow rules under the Nuclear Non-Proliferation Treaty despite its withdrawal from the treaty in 2003.

Thomas Countryman, assistant secretary of state for international security and nonproliferation, said NPT members will discuss the North Korea problem during the Preparatory Committee meeting for the 2015 Nuclear Non-Proliferations Treaty Review Conference underway in New York.

"The NPT requirements remain binding upon the DPRK," he said at a Foreign Press Center briefing via video conference from New York. The DPRK is the acronym for North Korea's official name, the Democratic People's Republic of Korea.

He cited Pyongyang's agreement in 2005 to return to the NPT "at an early date" and U.N. Security Council resolutions calling on the communist nation to act in accordance with rules that apply to NPT members.

Countryman stressed the seriousness of the "threat that North Korea poses not only to its neighbors and itself but to the nonproliferation treaty in the international nonproliferation regime."

He added the issue will be addressed "openly and forthrightly" in the PreCom session that opened Monday for a 12-day run.

North Korea acceded to the NPT in 1985 but announced its withdrawal in 2003.

In a 2005 landmark deal with its five dialogue partners -- South Korea, the U.S., China, Russia and Japan -- it agreed to return to the NPT at an early date and abandon all of its nuclear program in exchange for political and economic incentives.

But it has since conducted three known nuclear tests and claimed to be a nuclear state.

Countryman was emphatic that the NPT serves as a key element of international security and the basis for international nuclear cooperation.

"We will continue to address the serious challenges of cases of noncompliance with treaty obligations, and will continue to support expanding access to the peaceful uses of nuclear energy," he said.

Countryman is the chief U.S. delegate to the drawn-out negotiations with South Korea on revising their civilian nuclear cooperation.

The two sides have struggled to rewrite the so-called "123 agreement" amid Seoul's push to expand its non-military nuclear program.

Seoul wants to leave the door open for enriching uranium and reprocessing spent fuel some day.

Still, the Obama administration is concerned about a possible negative impact on its global nonproliferation drive.

The veteran diplomat avoided a direct answer to a question about whether such differences are being narrowed.

"I am negotiating a nuclear cooperation agreement with the Republic of Korea. But not this week," Countryman said. "We will conclude a nuclear cooperation agreement with the valued ally, the Republic of Korea, in the near future."

It would reflect the fact that South Korea is not only a vital partner of the U.S. but also is a leader in civil nuclear technology, he added. (Yonhap)