Japan's prime minister used a joint meeting of Congress on Wednesday to offer his condolences for the Americans who died during World War II, highlighting the close relationship since to urge lawmakers to back a contentious trade bill being negotiated by President Obama, Fox news reported.

Shinzo Abe's wide-ranging and historic speech was the first of its kind for a Japanese prime minister.

His speech comes as both countries mark the 70th anniversary of the end of World War II.

Coming close to a rare apology for Japan's actions during the war, he reflected on having visited the World War II Memorial in Washington and seeing the stars which represent lost Americans.

"History is harsh. What is done cannot be undone," he said. "With deep repentance in my heart, I stood there in silent prayers for some time."

He said: "On behalf of Japan and the Japanese people I offer with profound respect my eternal condolences to the souls of all American people that were lost during World War II."

The speech was part of a visit promoting Abe's staunch support of an even-tighter relationship between the former wartime adversaries in both trade and defense as the allies contend with a rising China.

The most immediate challenge is a trans-Pacific trade pact, which has pitted Obama against members of his own party and labor unions who have resisted it.

Abe, in his speech, urged all sides to "take the lead" in building a better market, and finish the 12-nation Trans-Pacific Partnership.

Since winning election in December 2012, Abe has been a strong advocate of closer ties with the US, an alliance that emerged from the ashes of World War II, which ended 70 years ago. He's been granted the full pomp and ceremony at the White House, and was being feted Tuesday night with a state dinner.