After threatening U.S., North Korea turns wrath on South

NEW: A Chinese state-run newspaper warns North Korea over nuclear test Pyongyang threatens "physical counter-measures" against South Korea It says it will act if South Korea takes a "direct part" in new U.N. sanctions A day earlier, the North said a new nuclear test would be part of its fight against the U.S.

Seoul, South Korea (CNN) -- In its latest bout of saber-rattling, North Korea on Friday warned of the possibility of "strong physical counter-measures" against South Korea in relation to tougher sanctions imposed this week by the United Nations.

The threat against South Korea came a day after the North said it would carry out a new nuclear test and more long-range rocket launches as part of a new phase of confrontation with the United States.

The statement Friday from North Korea's Committee for Peaceful Reunification of the Fatherland said it would take action against South Korea if it "takes a direct part" in the U.N. sanctions.

The South Korean Unification Ministry declined to comment specifically on the new threats from Pyongyang. It reiterated its stance that North Korea should refrain from further provocations.

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The two Koreas are technically still at war from the all-out conflict between them in the 1950s. Smaller scale clashes have occurred since then, most recently in November 2010 when North Korea shelled a South Korean island, killing several people.

South Korea and the United States are often the focus of menacing language from Pyongyang, but the latest U.N. sanctions, a response to a long-range rocket launched last month by the North, appear to have prompted a ratcheting up of the threats.

A displeased Chinese editorial

At the same time, North Korea's strong words and vow to conduct a third nuclear test -- previous ones took place in 2006 and 2009 -- appear to be testing the patience of its main ally, China, which voted in favor of the U.N. sanctions this week.

An editorial published Friday in the English-language edition of the state-run Chinese newspaper Global Times struck a displeased tone over Pyongyang's comments a day earlier.

"China's role and position are clear when discussing North Korea issue in the U.N. Security Council," the editorial said. "If North Korea engages in further nuclear tests, China will not hesitate to reduce its assistance to North Korea."

That prospect carries weight, since North Korea's impoverished economy relies heavily on China to stay afloat.

Global Times, whose editorial line often but not always reflects official Chinese policy, made it clear, though, that Beijing isn't about to cut Pyongyang loose.

"If the U.S., Japan and South Korea promote extreme U.N. sanctions on North Korea, China will resolutely stop them and force them to amend these draft resolutions," the editorial said.

Global Times noted that Beijing had put "a lot of effort into amendments" to the resolution approved by the Security Council this week.

"It seems that North Korea does not appreciate China's efforts," it said. "It criticized China without explicitly naming it in its statement yesterday."

The newspaper was referring to a passage in the controversial North Korean statement Thursday that said that "big countries, which are obliged to take the lead in building a fair world order, are abandoning without hesitation even elementary principle, under the influence of the U.S. arbitrary and high-handed practices."

The Global Times editorial also suggested that North Korea shouldn't rank too highly among China's priorities.

"China hopes for a stable peninsula, but it's not the end of the world if there's trouble there," it said, referring to the Korean peninsula that comprises North and South Korea. "This should be the baseline of China's position."

The Chinese Foreign Ministry on Thursday had urged North Korea and the West to "keep calm, remain cautious and refrain from any action that might escalate the situation in the region."

U.S. concerned but prepared

U.S. Secretary of Defense Leon Panetta said Thursday there are no "outward indications" that North Korea is about to conduct a nuclear test, but he admitted it would be hard to determine that in advance.

"They have the capability, frankly, to conduct these tests in a way that makes it very difficult to determine whether or not they are doing it," he said in a Pentagon press conference.

"We are very concerned with North Korea's continuing provocative behavior," Panetta said, but he added that the United States is "fully prepared" to deal with any provocations.