China appears to have dispatched two nuclear envoys to North Korea in what could amount to a last-ditch effort to keep Pyongyang from conducting another nuclear test.

Citing diplomatic officials in Beijing, former South Korean lawmaker Jang Sung-min said China's State Councilor Tang Jiaxuan and nuclear envoy Wu Dawei left China on Tuesday or early Wednesday, probably heading for Pyongyang.

"Both of the men are out of China" and apparently went to North Korea, Jang quoted the official as saying.

A North Korean official in Beijing confirmed that Tang visited North Korea as a special envoy, the South's Yonhap news agency said, without naming the official.

China is North Korea's last remaining ally and key aid donor, but it remains unclear whether Beijing could succeed in dissuading Pyongyang from testing another nuclear device, especially after Beijing supported a U.N. resolution that included punitive measures.

Ri Gun, director-general of the North Korean Foreign Ministry's American affairs bureau, did not rule out another test in an interview with a U.S. television network in Pyongyang that was broadcast Wednesday.

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"Even if there's a nuclear test, that is natural," Ri Gun said, without giving any further details.

In Washington, a veteran U.S. government arms control official told FOX News he believes North Korea will conduct a second nuclear test "sooner rather than later."

"If I was them, I would probably want to have another test, based on how the first test went," the official said of the North Koreans on condition of anonymity.

And while refusing to discuss classified intelligence, the source said he "wouldn't dispute" recent published reports claiming classified surveillance imagery has shown increased activity at North Korean nuclear sites, consistent with preparations for a nuclear test.

However, the official cautioned that a number of variables, including scientific, political, and economic factors, will affect Pyongyang's actions.

"You would not want to have a second failure," the official said, "so this argues for a later test. On the other hand, they might want a swift response to the Security Council [resolution], and that argues for sooner."

Jang, a former ruling party lawmaker who currently heads a policy think tank in Seoul, said the Chinese envoys could be poised to convey any North Korean message to U.S. Secretary of State Condoleezza Rice, who arrived in Tokyo Wednesday.

Rice, who plans to visit Beijing after a stop in Seoul, reassured Japan Wednesday that the U.S. is ready to use the "full range" of its military might to defend its Asian ally.

"The United States has the will and the capability to meet the full range — and I underscore the full range — of its deterrent and security commitments to Japan," Rice said following discussions with Japanese Foreign Minister Taro Aso.

Rice's words were a reminder to U.S. allies that the United States does not want to see a new nuclear arms race in Asia, but will likely be taken also as a warning to North Korea that it could face the U.S. nuclear arsenal if it used a nuclear weapon on a neighbor.

The United States has repeatedly said t does not intend to attack North Korea or topple its communist regime.

Shortly before Rice arrived, Aso said Japan should openly discuss whether it wants to possess nuclear weapons. He told a parliamentary committee the government has no plans to stray from its post-World War II policy of not allowing nuclear bombs on Japanese soil, "But I think it is important to discuss the issue."

Even discussing the issue is extremely sensitive in Japan, with its troubled military history and experience as the only nation where nuclear weapons were used in wartime.

With Rice at his side, Aso did not repeat the need for a discussion.

"The government is absolutely not considering a need to be armed by nuclear weapons," Aso said. "We do not need to acquire nuclear arms with an assurance by Secretary of State Rice that the bilateral alliance would work without fault."

Later Wednesday, Japanese Prime Minister Shinzo Abe insisted his government would not even discuss building a nuclear bomb.

"That debate is finished," Abe testily told reporters.

It was at least the third time since North Korea's test that Abe — a hawk on defense issues who came to office last month promising a more assertive Japan — has had to reassure jittery neighbors and an anxious United States that Tokyo would not abandon its postwar ban on nuclear weapons.

In addition to settling nerves among allies, Rice's Asia trip is meant to reinforce pressure on South Korea and especially China to enforce economic sanctions. Those include what the United States describes as an aggressive inspection and interdiction program that stops short of a full blockade of North Korean trade.

The Associated Press contributed to this report.