A Japanese Foreign Ministry official warned of tougher measures against North Korea on Friday if the isolated communist nation conducts a second nuclear test in the face of international condemnation. The remarks came amid U.S. media reports saying that Pyongyang has appeared to have readied for another nuclear test and that the preparation steps were similar to those taken before its first nuclear detonation on Oct. 9.

Officials in Japan and South Korea said earlier Friday they saw no particular signs that the North was readying for a second test, but Tokyo urged its neighbor to refrain from any developments that would stoke regional tensions.

"We think it is essential that North Korea should stop further nuclear testing and they should abandon all their nuclear programs," said Nori Shikata, assistant press secretary for Japan's Foreign Ministry. "If they conduct another nuclear test, then the international community, including Japan, will take additional measures."

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Shikata did not give specifics about what additional steps might be taken, but said they would be pursued through the United Nations, which authorized trade restrictions against North Korea after its October test.

Any additional moves would be met with what Japan calls the "pressure approach," Shikata said.

Speculation about a second test comes just weeks after international talks aimed at ending Pyongyang's nuclear weapons program ended without a breakthrough. North Korean nuclear envoy Kim Kye Gwan said in December that his country would bolster its atomic arsenal and further improve its deterrent in response to international pressure.

The North has hailed its Oct. 9 test as "an auspicious event in the national history," and says it serves as a key deterrent against a possible U.S. attack. Washington has repeatedly denied that it plans to invade.

ABC News reported Thursday that North Korea appeared ready for another test, citing unidentified U.S. defense officials.

Click here to view the ABC News story.

"Some unidentified activities have been detected around a suspected test site but so far there are no particular indications directly linked to an additional nuclear test," Cho Hee-yong, a spokesman for South Korea's Foreign Ministry, said.

A Western diplomat based in Seoul who is close to North Korean affairs also dismissed the ABC report, saying no specific evidence or movement has been detected to suggest test preparations, according former South Korean lawmaker Jang Sung-min.

Jang declined to identify the diplomat, citing the sensitivity of the issue.

In Tokyo, Japan's top government spokesman refused to comment on Tokyo's intelligence gathering.

"We gather every possible piece of intelligence on these matters, and exchange information with the involved nations through close contact, but refrain from commenting on our judgment of its content," Chief Cabinet Secretary Yasuhisa Shiozaki said.

However, a Defense Agency spokeswoman — speaking on condition of anonymity as per agency policy — said the agency had not seen any information that would indicate test preparations were under way.

Meanwhile, a South Korean military intelligence official said vehicle and personnel activities are constantly spotted at a suspected test site but that it was too early to say whether they indicated an imminent nuclear test, Yonhap news agency reported.

The official, whom Yonhap didn't name, also said no power outlets or communication cables have been detected at the suspected site.

South Korea's Joint Chiefs of Staff said it cannot comment on intelligence matters.

In 2005, North Korea pledged to dismantle its nuclear program in exchange for security guarantees and aid but no progress has been made in implementing that accord.

A key sticking point at the international talks has been North Korea's demand that the U.S. lift financial restrictions imposed on it in response to the impoverished nation's alleged counterfeiting of US$100 bills and money laundering.