AFP - North Korea fired another short-range missile on Friday and threatened fresh steps if world powers impose sanctions for its nuclear test, amid signs it may be readying a new long-range launch.
The United States said it was sending its North Korea envoy to the jittery region, where Chinese fishing boats were fleeing a sensitive part of the Yellow Sea in fear of potential naval clashes.
The communist North, which has warned it could launch an attack on the South, vowed to respond to any fresh sanctions imposed by the United Nations.
"If the UN Security Council provokes us, our additional self-defence measures will be inevitable," the North's foreign ministry said in a statement carried by official media.
"The world will soon witness how our army and people stand up against oppression and despotism by the UNSC and uphold their dignity and independence."
Tensions have been running high since Kim Jong-Il's regime said it tested a nuclear bomb on Monday for the second time and renounced the armistice that ended the Korean War in 1953.
North Korea test-fired another missile off its east coast Friday, the sixth this week, according to South Korea's Yonhap news agency.
There was no immediate confirmation but the agency's reports of five launches earlier this week were later confirmed by Pyongyang.
In Washington, two US defence officials said that satellite photos suggest North Korea may now be preparing to launch a long-range ballistic missile.
Vehicle movements at a missile site resemble work done before North Korea fired a long-range rocket last month, the officials told AFP on condition of anonymity.
With US and South Korean troops on high alert, US Defence Secretary Robert Gates was due to consult his counterparts from South Korea and Japan on Saturday at a regional conference in Singapore.
Stephen Bosworth, the US special envoy on North Korea, and Deputy Secretary of State James Steinberg will head Sunday to Tokyo and later visit China, South Korea and Russia, the State Department said.
The countries were part of six-nation talks that agreed in 2007 to provide aid and security guarantees to North Korea in return for denuclearisation.
Pyongyang stormed out of the accord last month in protest after the UN Security Council unanimously condemned its long-range missile launch.
The Council has been discussing a potential resolution -- stronger than last month's statement -- to condemn the North's nuclear test. But it was not yet clear if that would include new sanctions.
Gates, en route to Singapore, accused the North of "very provocative, aggressive" actions. But he also tried to calm nerves, stressing the United States was not planning any military action.
Gates said he was unaware of any unusual troop movements in the North, which has around 1.1 million soldiers, compared with 680,000 South Korean and 28,500 US troops south of the border.
"I don't think there is a need for us to reinforce our military presence in the South. Should the North Koreans do something extremely provocative militarily, then we have the forces to deal with it," he added.
The North may take further steps following its latest verbal statement, which aims to send a "strong warning" to the Security Council, said Professor Yang Moo-Jin at Seoul's University of North Korean Studies.
"The North may put its military on a war footing, test-fire a long-range missile and restart the plutonium reprocessing facilities at Yongbyon," he told AFP.
The North could also stage a third nuclear test but this would come much later than the other steps, Yang said.
In a possible sign of trouble ahead, Chinese fishing boats were leaving the tense border area in the Yellow Sea where the two Koreas fought deadly naval clashes in 1999 and 2002, South Korea's defence ministry said.
"As this could be a signal foreboding a possible provocation by the North, we are watching the situation closely," ministry spokesman Won Tae-Jae said.
Pyongyang warned Wednesday it could not guarantee the safety of US or South Korean ships after Seoul said it was joining a US-led international effort to stop the trade in weapons of mass destruction.
But some experts question North Korea's military capabilities. A US official in Washington said on condition of anonymity that initial US radioactivity tests had not yet confirmed Pyongyang's nuclear test.