SEOUL, South Korea — North Korea threatened to retaliate if punitive U.N. sanctions are imposed for its latest nuclear test, and U.S. officials said there are new signs Pyongyang may be planning more long-range missile launches.
Washington warned on Saturday the U.S. would respond quickly to any moves that threaten America or its Asian allies.
"We will not stand idly by as North Korea builds the capability to wreak destruction on any target in Asia _ or on us," U.S. Defense Secretary Robert Gates said at a regional defense meeting in Singapore. The Associated Press obtained an advance copy of his speech.
With tensions rising, the communist nation punctuated its barrage of rhetoric with yet another short-range missile launch on Friday _ the sixth this week.
Perhaps more significantly, officials in Washington said there are indications of increased activity at a site used to fire long-range missiles. The officials spoke on condition of anonymity because methods of gathering information about North Korea are sensitive.
U.S. spy satellites detected signs the North was preparing to transport a long-range missile by train to its northeastern Musudan-ni launch pad, an official at South Korea's Defense Ministry said Saturday. The official, who spoke on customary condition of anonymity, said the missile was from an armament factory near Pyongyang.
South Korea's Yonhap news agency said the latest test launch Friday was a surface-to-air missile designed to defend against aircraft or other missile attacks. It said the missile was believed to be a modified version of the Russian SA-5.
The nuclear test and flurry of missile launches, coupled with the rhetoric from Pyongyang that it won't honor a 1953 truce ending the fighting in the Korean War, have raised tensions in the region and heightened concerns that the North may provoke a skirmish along the border or off its western coast _ the site of deadly clashes in 1999 and 2002.
But officials said the heavily fortified border remains calm and the U.S. defense secretary said Washington does not see the situation as a crisis warranting any more troops to augment the 28,000 U.S. forces already in South Korea.
North Korea remained strident.
"There is a limit to our patience," its Foreign Ministry said in a statement carried on the North's official Korean Central News Agency. "The nuclear test conducted in our nation this time is the Earth's 2,054th nuclear test. The five permanent members of the U.N. Security Council have conducted 99.99 percent of the total nuclear tests."
North Korea said it conducted the test in self-defense. It has asserted the United States is planning a pre-emptive strike to oust the regime of leader Kim Jong Il and warned it would not accept sanctions or other punitive measures being discussed by the Security Council.
"If the U.N. Security Council makes a further provocation, it will be inevitable for us to take further self-defense measures," the Foreign Ministry said. It reiterated that it no longer sees the truce as valid, but it has made that claim several times in the past.
The draft of a U.N. resolution being negotiated in response to the North's second nuclear test calls on all countries to immediately enforce sanctions imposed after the North's first test in 2006.
They include a partial arms embargo, a ban on luxury goods, and ship searches for illegal weapons or material. The sanctions have been sporadically implemented, with many of the 192 U.N. member states ignoring them.
The partial draft, obtained Friday by The Associated Press after it first appeared on the Inner City Press Web site, would have the council condemn the North's May 25 nuclear test "in the strongest terms ... in flagrant violation and disregard" of the 2006 resolution.
A list of proposals was sent Wednesday to the five permanent veto-wielding council members _ the U.S., Russia, China, Britain and France _ and the two countries most closely affected by the nuclear test, Japan and South Korea.
U.S. officials said Friday its initial air sampling from near the underground test site was inconclusive. At least one more test will be conducted.
North and South Korea technically remain at war because they signed a truce, not a peace treaty, in 1953. North Korea disputes the U.N.-drawn maritime border off its west coast and has positioned artillery guns along the west coast on its side of the border, Yonhap said.
From the South Korean island of Yeonpyeong, about a dozen Chinese ships could be seen pulling out of a North Korean port and heading elsewhere, possibly to avoid any skirmishes.
Yonhap reported that more than 280 Chinese fishing vessels were in the area earlier this week, but the number is now about 140. It was not clear if the Chinese vessels, in the area for the crabbing season, were told by the North to leave or if they did so on their own.
South Korean and U.S. troops facing North Korea raised their surveillance Thursday to its highest level since 2006, when the North first tested a nuclear device.
A squadron of F-22 stealth fighters _ the most advanced in the U.S. Air Force _ were due to arrive Saturday on the southern Japan island of Okinawa, and Friday's missile launch may have been the North's attempt to show it has the means to shoot them down, or at least make any incursion into its airspace risky.
Its other launches this week were of land-to-sea missiles, a warning that it can strike warships that come too close.
Talmadge reported from Seoul, National Security Writer Gearan reported from Washington; Associated Press writers Jae-soon Chang in Seoul, Lara Jakes aboard a U.S. military jet, National Security Writer Robert Burns in Washington, and Edith M. Lederer at the United Nations contributed to this report.