SEOUL North Korea, pressing ahead with a rocket launch in defiance of a U.N. resolution, is also preparing a third nuclear weapons test, South Korean news reports said on Sunday, a move bound to scare neighbors and infuriate the West.
South Korea's Yonhap news agency quoted an unidentified intelligence source as saying North Korea was "clandestinely preparing a nuclear test" at the same location as the first two.
The source added that workers in the destitute North had been seen in commercial satellite images digging a tunnel in the northeastern town of Punggye-ri, Kilju County, in addition to existing mines believed to have been used for tests in 2006 and 2009.
"We have confirmed the (mining) work is coming to its final stage," the source was quoted as saying.
The satellite imagery showed piles of earth and sand at the entrance of the tunnel, Yonhap said.
North Korea, which three years ago pulled out of six-party disarmament talks on its nuclear program, agreed in February to stop nuclear tests, uranium enrichment and long-range missile launches in return for food aid, opening the way to a possible resumption of the negotiations.
But that has all since unraveled with the North's rocket launch planned for this month, probably between Thursday and the following Monday. The North says it is merely sending a weather satellite into space, but South Korea and the United States say it is a ballistic missile test.
Two previous launches of the long-range missile have failed, but Washington says the North's missile program is progressing quickly and that the American mainland could come under threat within five years.
U.S. President Barack Obama last month called on North Korea to curb its nuclear ambitions or face further international isolation.
He said North Korea could be hit with tighter sanctions if it goes ahead with the launch, but experts doubt China will back another U.N. Security Council resolution against it.
China, Japan and South Korea, three of the "six parties" along with the United States and the two Koreas, on Sunday expressed concern over the planned launch.
The foreign ministers of the three countries, ending their annual meeting with a joint news conference in the coastal Chinese city of Ningbo, largely stuck to established positions.
"China expresses our concern for the development of the situation and urges all relevant parties to take into consideration the bigger picture and think long-term," Chinese Foreign Minister Yang Jiechi said.
Obama has urged China to use its influence to rein in North Korea instead of "turning a blind eye" to its "deliberate provocations".
Japan and South Korea reiterated warnings that Pyongyang would face international consequences if it went ahead with the launch.
"I made it clear that the international community needs to make rigorous responses against North Korea's violation of its obligation as a member country in the world community," South Korean Foreign Minister Kim Sung-hwan said.
Japanese Foreign Minister Koichiro Gemba said the launch would roll back progress Pyongyang has made in talks with various countries, including with the United States, which has suspended the planned food aid.
(Reporting by Sean Shim in Seoul and Roystan Chan in Ningbo; Writing by Michael Martina and Nick Macfie)