A U.S. soldier in Japan has apologized over a deadly hit-and-run accident, his lawyer said Friday, in a high-profile case that comes amid a bilateral row over American military bases.

A U.S. soldier suspected of being involved in a fatal hit-and-run accident in Japan's southern island of Okinawa has refused further questioning by Japanese police, a U.S. Army officer and Japanese police said Thursday.

Four people were injured when a passenger riding on a Tokyo subway train accidentally broke a bottle of hydrochloric acid he was carrying, media and the train company said on Wednesday.

Japan's foreign minister said Monday that Tokyo should honor its agreement to find a new location for a major U.S. Marine base, but he and the prime minister said they were still seeking options on where it should go.

Barack Obama insisted on Friday that the United States was a “Pacific” power and vowed to deepen its engagement in the region as he set foot in Asia for the first time as U.S. president.

U.S. President Barack Obama and Japanese Prime Minister Yukio Hatoyama promised on Friday close cooperation on nuclear non-proliferation and Japan agreed to host a conference in January on nuclear security.

President Barack Obama aimed Friday to shore up relations with a new Japanese government vowing to be more assertive with its U.S. ally, even as he grapples with sending more U.S. troops to Afghanistan.

Japan's Emperor Akihito, celebrating 20 years on the throne Thursday, offered a rare defence of his father's wartime record, saying Japanese aggression had been contrary to his wishes.

Tens of thousands of well-wishers lined the streets of Tokyo on Thursday for a parade on the 20th anniversary of the coronation of Emperor Akihito, who urged Japanese not to forget the lessons of World War II.

The United States and Japan will agree this week to review their decades-old security alliance to tighten ties long term, a Japanese newspaper said Wednesday, as the two countries struggled to keep a feud over a U.S. military base from spoiling their leaders' summit.