Tokyo ? The United States is willing to use its full military might to defend Japan in light of North Korea’s nuclear test, Secretary of State Condoleezza Rice said Wednesday as she sought to assure Asian countries there is no need to jump into a nuclear arms race.

At her side, Rice’s Japanese counterpart drew a firm line against his nation developing a nuclear bomb.

The top U.S. diplomat said she reaffirmed President Bush’s pledge, made hours after North Korea’s Oct. 9 underground test blast, “that the United States has the will and the capability to meet the full range – and I underscore the full range – of its deterrent and security commitments to Japan.”

Rice spoke following discussions with Japanese Foreign Minister Taro Aso, the first stop on her crisis mission to respond to the threat posed by the North.

Back home, President Bush told ABC News that if the U.S. learned North Korea was about to transfer nuclear technology to others, the communist nation would face “a grave consequence.” He did not elaborate.

“I want the leader to understand – the leader of North Korea to understand that he’ll be held to account,” Bush said, referring to ruler Kim Jong Il.

Signs continued Wednesday that North Korea might be readying for a second nuclear test that could be carried out as soon as this week, while Rice is in Asia.

China’s president, Hu Jintao, apparently has sent a special envoy to North Korea, according to a former South Korean lawmaker, Jang Sung-min, citing diplomatic officials in Beijing. Rice planned to see the Chinese official, State Councilor Tang Jiaxuan, this week in Beijing.

There were reports that North Korea had told China it was ready to conduct up to three more nuclear tests. But at the State Department in Washington, spokesman Tom Casey said, “We certainly haven’t received any information from them, from the Chinese, that they’ve been told by Pyongyang that another test is imminent.”

Rice’s reference to U.S. willingness to honor the “full range” of the nation’s security commitments was meant as a signal to allies that the United States does not want to see them embarking on a new nuclear arms race to protect themselves. It was also likely to be taken as a reminder to North Korea that, should it use nuclear weapons on a neighbor, the U.S. has powerful forces of its own – including nuclear – and is pledged to defend its friends in the region.