Chief Cabinet Secretary Yasuhisa Shiozaki also suggested there would be no further apology from Tokyo on the wartime brothels, despite the passage of the resolution by the House Foreign Affairs Committee.
"The alliance between the U.S. and Japan is irreplaceable. There is no change at all to the fact that Japan-U.S. relations will continue to be unshakable," Shiozaki said.
The committee approved the nonbinding resolution by a 39-2 vote on Tuesday. It urges Japan to "formally acknowledge, apologize and accept historical responsibility in a clear and unequivocal manner" for the suffering of "comfort women" during the 1930s and 1940s.
The endorsement allows the measure to be considered by the full House of Representatives.
Prime Minister Shinzo Abe refused to comment on the passage of the resolution, saying it was a matter for the U.S. Congress.
"I have already explained my thinking when I visited the U.S.," Abe told reporters.
Shiozaki said there has been no change in Tokyo's stance.
"The government's position on the comfort women issue is clear from the prime minister's recent visit to the U.S. in April. I have nothing more to add," Shiozaki said, referring to an apology by Abe during his U.S. trip for the sex slaves' suffering.
Historians say hundreds of thousands of women, mainly from Korea, China and the Philippines, were sent to Japanese military brothels in the 1930s and '40s. Many victims say they were forced to provide sexual services against their will to Japanese soldiers.
Abe triggered controversy in March when he said there was no evidence that the women had been coerced into working as prostitutes, and he said Japan would not make a further apology in reaction to the U.S. resolution.
Abe, facing international criticism, later said he stood by an earlier Japanese government apology, saying he sympathizes with the victims' plight and regrets the "situation they found themselves in."
One of the former sex slaves, now living in Australia, welcomed the U.S. resolution Wednesday and said she hopes Japan will finally apologize for forcing her and thousands of other women to work as sex slaves.
"It would be fantastic for the comfort women, late in our lives and after all these years, to get this finalized with an apology," Jan Ruff O'Herne, an 84-year-old former Dutch colonist born in Indonesia, said in the Australian city of Adelaide.
A lobbying group also welcomed the resolution.
"We applaud the good act of the Foreign Relations Committee with deep gratitude," the Japan Action Network for the Issue of Military Sexual Slavery said in a statement.
"It is our sincere hope that the resolution will pass at the House of Congress in due time, announcing ... that the international community would not tolerate the Japanese government neglecting the human rights of the victims," it said.
Two 86-year-old Taiwanese women demonstrated outside Japan's representative office in Taipei on Wednesday, demanding that the Japanese government apologize for forcing them into sexual slavery.
Also on Wednesday, 44 lawyers representing some of the sex slaves in lawsuits seeking compensation from the government submitted a letter addressed to the Japanese prime minister urging new measures to settle the issue. The lawyers want talks between the government and the victims.
"International criticism against Japan on the resolution of the comfort women issue is increasing. Rather than being told from outside, it's necessary for Japan to see this issue as its own challenge," lawyer Shiro Kawakami told reporters.
"Now is the chance for Japan to take concrete measures for the future," he said.
After decades of denial, the Japanese government acknowledged its role in wartime prostitution after a historian discovered documents showing government involvement. In 1993 the government issued a carefully worded official apology.