U.S. says North Korea test results 'inconclusive'

Initial U.S. testing to determine whether North Korea fired a nuclear device on Monday proved "inconclusive," said a U.S. official on Friday.

"The first test results came in inconclusive. They did not find anything that could confirm a nuclear device was detonated," said the U.S. official, who declined to be named.

The statement came hours after North Korea defiantly test-fired another short-range missile Friday and warned it would take self-defense action if provoked by the UN Security Council, which is considering tough sanctions against the communist regime for conducting a nuclear test.

The launch was the sixth short-range missile North Korea has test-fired since its nuclear test on Monday.

Pyongyang's Foreign Ministry said in a statement earlier Friday that the country won't recognize any Security Council resolutions unless the council first apologizes for criticizing Pyongyang's April 5 rocket launch.

"If the UN Security Council makes a further provocation, it will be inevitable for us to take further self-defense measures," the North's Foreign Ministry said in a statement carried by the official Korean Central News Agency.

The statement called the council hypocrites.

"There is a limit to our patience," the statement said. "The nuclear test conducted in our nation this time is the Earth's 2,054th nuclear test. The five permanent members of the UN Security Council have conducted 99.99 percent of the total nuclear tests."

The North has been strident since its test - which it has also called a self-defensive measure. It did not specify what further action it was considering in response to UN resolutions, nor what it would consider a provocation.

Japan's United Nations ambassador Yukio Takasu said negotiators held a "good discussion" Thursday on possible tough measures against North Korea for detonating a nuclear device and firing a string of missiles this week despite international protests.

The closed-door discussion was held by the five UN Security Council permanent members - the United States, Russia, France, China and Britain - plus Japan and South Korea for at least the second time this week since Pyongyang conducted the nuclear test on Monday.

Takasu told reporters after the meeting: "It was agreed among the group that sensitive matters are now being handle in consultations and we agree that we should not, at this time, share them with the media."

"We are doing very good work. There has been a good understanding and cooperation among the group that the UN Security Council must respond clearly and strongly as soon as possible," Takasu said.

While avoiding speaking on behalf of China, he said that Beijing "understands the situation and is working very constructively" with the group.

Japan in particular has called for new, tough measures against North Korea in addition to the set of comprehensive sanctions imposed on North Korea after it detonated its first nuclear bomb in 2006.

Those sanctions include an embargo on sales of weapons and nuclear technology to North Korea, a freeze of assets and resources owned by North Korea abroad and a ban on travel for certain regime officials.

In Washington, the U.S. State Department announced Thursday that Deputy Secretary James Steinberg would visit Japan next week with the North Korean nuclear issue on the agenda. He was due to be there Monday-Wednesday for meetings with senior Japanese officials.

Steinberg will head to Tokyo after Friday-Sunday meetings in Singapore for the Shangri-La Dialogue on East Asian security trends.

Meanwhile, Chinese fishing ships are quitting a disputed sea border that divides the two Koreas as tension mounts on the peninsula following this week's nuclear test by the North, South Korean media reported on Friday.

South Korea and the United States earlier raised the military alert level in the region as North Korea turns increasingly belligerent, following its nuclear test and the threat of war.

"Chinese fishing vessels have begun retreating from NLL (northern limit line) waters since yesterday. We are working to find out if this is based on North Korea's request," Yonhap news agency quoted an unnamed South Korean army source as saying.

The NLL marks the maritime border between the two Koreas.

Two deadly naval battles have been fought nearby in the past 10 years and the North has warned another could happen soon in what is one of the last major flashpoints from the Cold War.

The clashes in 1999 and 2002 were in June, the peak of the lucrative three-month-long crab season and when fishing fleets jockey for the best spots near the contested maritime border.

The joint command for the 28,500 U.S. troops that support South Korea's 670,000 soldiers has raised its alert a notch to signify a serious threat from North Korea.

That is the highest threat level since the North's only other nuclear test in October 2006. It calls for stepped up surveillance but not an increase in military maneuvers.

The troops face a more than million-strong North Korean military, most of them massed near the heavily-fortified border.