North Korea appears to be preparing for a third nuclear test as early as next March, a South Korean newspaper has reported, as a US politician travelled to Pyongyang with a message for it to "calm down".
US and South Korean intelligence have been watching North Korea's nuclear sites for any activity. Analysts say it could use a test to try to gain leverage in the international talks it wants, and to secure aid to prop up its destitute economy.
South Korea's Chosun Ilbo daily cited an intelligence official from Seoul as saying a tunnel was being dug at a North Korean nuclear test site that could be completed in March next year, possibly heralding a new test.
South Korea's foreign ministry said it was closely monitoring the site and had found no concrete evidence of such preparations.
The governor of New Mexico, Bill Richardson, is on his way to North Korea as an unofficial envoy. "My objective is to try to get North Korea to calm down a bit, see if we can reduce tension in the Korean peninsula," he was quoted by the BBC as saying before he left the US.
The amount of earth removed from the site at Punggye township, in north-eastern North Korea, indicated the tunnel was about 500 metres deep, half the depth needed for a nuclear test, the Chosun Ilbo report said.
"North Korea is digging the ground pretty hard … at its two major nuclear facilities," a South Korean intelligence official was quoted as saying.
"At this rate [the Punggye tunnel] will reach [the] 1km that is needed for a nuclear test by March to May," a separate intelligence source told the newspaper.
North Korea is speeding up construction work at its main Yongbyon nuclear complex, where it revealed a previously unknown uranium enrichment facility last month, the newspaper quoted intelligence sources as saying.
South Korea's foreign ministry declined to confirm the details of the report, and said: "Nothing has been confirmed that would prove the north is preparing to conduct a nuclear test."
South Korea's nuclear envoy, Wi Sung-lac, was in Moscow meeting his Russian counterpart in the same week that the Russian foreign minister, Sergei Lavrov, met North Korea's foreign minister, Pak Ui-chun, and chided him over the north's nuclear programme.
South Korea held its largest civil defence drill in recent years today. The exercise on a busy weekday brought traffic to a standstill throughout the country and saw mass evacuations to bomb shelters.
The prime minister, Kim Hwang-shik, said the aim was to heighten readiness for a possible North Korean air raid. He warned the north to expect reprisals if there was another attack. Last month North Korea shelled an island near their disputed maritime border, killing four people.
"The government is ready to demonstrate that there will be due price to pay for any future aggression," he said.
The deputy US secretary of state, James Steinberg, has travelled to Beijing to consult with the Chinese on North Korea.
North Korea showed a uranium enrichment facility, which could give it a second route to make nuclear bombs, at the Yongbyon site to a US expert last month and later announced it was operating a "peaceful" energy project. South Korea's foreign minister said yesterday he suspected North Korea had more uranium enrichment plants. A media report said Pyongyang had three or four.