Japan's PM Shinzo Abe has said comments he made in March, which appeared to minimise Japan's role in World War II sex slavery, were misunderstood.
Mr Abe and his wife had dinner at the White House
Speaking during his first trip to the US as leader, Mr Abe said he felt deep sympathy for wartime "comfort women".
As part of his Washington visit, Mr Abe also met US President George Bush for an informal dinner at the White House.
The two men talked about baseball and golf, but the discussions will turn to more serious matters on Friday.
The leaders are expected to meet at Camp David to discuss bilateral ties and co-operation over North Korea.
Mr Abe provoked an angry reaction in March, when he questioned whether there was any proof that the Japanese military coerced women to work as sex slaves during World War II.
But he has since stated several times that he stands by an official 1993 statement in which Japan acknowledged the imperial army set up and ran brothels for its wartime troops.
Mr Abe tried to minimise the damage further on Thursday, when he told US lawmakers: "I feel sympathy from the bottom of my heart to former comfort women."
"I feel deeply sorry that they were forced to be placed in such extremely painful situations," he was quoted as saying by Japanese government officials.
"I believe my remarks and true intentions were not conveyed accurately [last month]," Kyodo news agency quotes him as saying.
Republican Representative Roy Blunt also said Mr Abe "expressed regret that his comments were not as he intended for them to be".
Before leaving for the US, Mr Abe said he hoped to build a relationship with Mr Bush "in which we can discuss everything frankly".
"The Japan-US alliance is the cornerstone of Japan's diplomacy and national security and as unshakable, irreplaceable allies, we need to build a firm relationship of trust," he told reporters.
ON THE AGENDA
North Korea's nuclear programme
Abduction of Japanese citizens by North Korea
Joint ballistic missile defence system
Realignment of US troops in Japan
Japan's support for Iraqi reconstruction
Changes to Japan's pacifist constitution
Greater co-operation over climate change
Japan's easing of restrictions on US beef imports
Mr Abe is known for being a hardliner on North Korea and, in particular, its abduction of Japanese citizens in the 1970s and 80s.
He said he would discuss the need to "find a solution to the issues of nuclear arms, missiles and abductions" in co-operation with other nations.
"I will express my stance with an iron will of seeking a solution to the abduction issue," he went on.
High on the agenda will also be the two countries' military relationship, as well as climate change, Iraq and Japan's decision to ease restrictions on US beef imports.
Correspondents say Mr Abe's visit will be subdued in comparison to that of his flamboyant predecessor Junichiro Koizumi, who had a close relationship with Mr Bush.
On Mr Koizumi's last visit before leaving office, he wowed Americans with an Elvis Presley impersonation on a sideline visit to Graceland.
Mr Abe chose to broaden Japanese diplomacy when he took office, by breaking with a tradition that the new Japanese prime minister's first overseas visit be to Washington.
Instead, he went to China and South Korea in a bid to ease strained ties.
He met Mr Bush for the first time in November, on the sidelines of a Pacific Rim summit in Vietnam.
Mr Abe's visit to the US will also include a trip to the Arlington National Cemetery and dinner at the White House before he leaves for a five-nation tour of the Middle East.