Condoleezza Rice told Japan on Wednesday that Washington would stand by its commitment to protect its Asian ally, where North Korea's atomic test has stirred debate about acquiring nuclear weapons.
"The United States has the will and the capability to meet the full range, and I underscore full range, of its deterrent and security commitments to Japan," Rice told a news conference in Tokyo, the first stop on a quick tour of North Asia.
Earlier in the day, Taro Aso, the Japanese foreign minister, said that Japan should openly discuss whether it wants to possess nuclear weapons.
Japan's government, however, had no plans to stray from its postwar policy of not possessing, developing or allowing nuclear bombs on Japanese soil, Aso told a parliamentary committee on Wednesday.
Possessing nuclear weapons is a sensitive political issue in Japan, the only nation to have suffered a nuclear attack. US atomic weapons destroyed the cities of Hiroshima and Nagasaki in 1945 near the end of the second world war.
Aso told a lower house panel on foreign affairs: "When a country next to us comes to have [nuclear weapons], we can't consider, we can't talk, we can't do anything and we can't exchange opinions. That's one way of thinking.
"I believe it is important to have various discussions on it as one more way of thinking."
No change of policy
Aso said Tokyo had no plans to develop the weapons, though he suggested to the committee that it was odd that Japan had never openly discussed it.
"Japan's position to stick to its three non-nuclear principles will not change," he said.
"But the issue of nuclear possession has been discussed by many people for decades, and it is only in Japan where the discussion about its own nuclear possession is completely absent."
Since North Korea's test, Shinzo Abe, Japan's prime minister, has said that Japan would not change its non-nuclear policy, despite North Korea's October 9 detonation of an atomic device.
"Possession of nuclear arms is not an option at all for our country," Abe told parliament last week.
Rice arrives in Japan
Condoleezza Rice and Taro Aso reaffirmed the US-Japan alliance
Rice said she was trying to find a regional solution to the North Korea nuclear crisis.
"The United States has no desire to escalate this crisis. We would like to see it de-escalate," she told reporters at a joint news conference with Aso on Wednesday afternoon.
Rice reaffirmed Washington's commitment to the defence of Japan, its most important ally in the region and home to 50,000 US troops.