Japan pressed on with efforts on Thursday to secure a UN condemnation of North Korea's nuclear test threat after Washington, in its starkest warning so far, said it would not live with a nuclear-armed Pyongyang.
North Korea's neighbours, including China - the closest the reclusive Stalinist state has to an ally - hardened their response to Tuesday's announcement, in contrast to their disunity over missile tests carried out by Pyongyang three months ago.
Japan's Kyodo news agency reported from New York that Chinese Foreign Minister Li Zhaoxing had warned North Korea it would face "serious consequences" if it made good on its pledge to test a nuclear device.
Quoting diplomatic sources, it said Li had conveyed the warning from China's top leadership to North Korea's ambassador in Beijing. A Chinese Foreign Ministry spokeswoman said she could not confirm the report. Publicly, the foreign ministry has called only for restraint on North Korea's part and for other countries to avoid actions that would heighten tensions.
But citing "informed sources", Kyodo said late on Thursday that a US military aircraft capable of collecting and analysing airborne radioactive substances had earlier taken off from the Kadena base in Okinawa.
The reported hardening of Beijing's tone came as Japan - perhaps ceding ground to China - signalled a willingness to accept a less formal UN Security Council warning than the "presidential statement" it has sought along with the United States and France.
The proposed statement would warn North Korea that if it went ahead with a test, the council would impose consequences, although it does not specify what those should be. China, however, wants the issue resolved through six-country talks set up to end North Korea's nuclear weapons programme.
Japan's chief cabinet secretary, Yasuhisa Shiozaki, told a news conference on Thursday that Tokyo was now ready to accept a "press statement" from the United Nations for the sake of a speedy and united condemnation.
"A president's press statement would quickly send a united message from international society," he said. "Debate will resume (at the United Nations) tonight, and we hope that they'll discuss (it) thoroughly and come to a decision."
Japan's new prime minister, Shinzo Abe, is due to visit Beijing on Sunday and Seoul the following day to break the ice in relations between Tokyo and its neighbours left by his predecessor, Junichiro Koizumi.
"Seeing the new diplomatic overtures between China, South Korea and Japan is probably ratcheting up North Korean concerns," said Brad Glosserman, executive director at the Hawaii-based Pacific Forum CSIS.