U.S. Congressman Mike Honda, who has been at the forefront of efforts to help victims of Japan's wartime sexual slavery, said this week's breakthrough deal on the issue between Seoul and Tokyo is far from perfect, but is still a "historic milestone."

Honda, however, expressed disappointment that the agreement lacks a commitment by Japan to "ensure they will no longer whitewash history and educate future generations" and that Tokyo's apology as part of the deal is "not a formal, and official apology issued by the Japanese Diet."

The agreement "is far from perfect but it is indeed, a historic milestone, a step in the right direction, and one which I sincerely hope, will finally restore the dignity and honor of the 200,000 girls and women who were sexually enslaved during World War II," Honda said in a statement.

On Monday, South Korean Foreign Minister Yun Byung-se and his Japanese counterpart, Fumio Kishida, reached the agreement in talks in Seoul earlier in the day, which centers on Japan's admission of responsibility for the wartime crime and plans to pay reparations to the victims.

The deal removes the biggest thorn in relations between Seoul and Tokyo, and offers hope not only for greater cooperation between the two neighbors, but also for significant progress in U.S. efforts to forge stronger security cooperation with the two allies in a region marked by a rising China.

Honda emphasized the urgency of resolving grievances of victims.

"In 2015 alone, nine Korean 'comfort woman' passed away. They passed away without seeing the light and hope of this agreement.

Thousands more passed away across the Asia-Pacific region without a promise of closure, justice, or peace," he said.

He also urged Japan to stop attempting to whitewash its wartime past.

"I am deeply disappointed this agreement lacks a commitment by Japan to ensure they will no longer whitewash history and educate future generations. Only by educating our future generations, can we commit to upholding the human rights of all, and ensuring the wrongs of history will never repeat," Honda said.

"I urge Prime Minister Abe and the government of Japan to fully commit to this education and ensure this atrocity never happens, ever again. I am also disappointed this apology is not a formal, and official apology issued by the Japanese Diet," he said.

Under Monday's deal, Japan formally acknowledged its responsibility for forcing Korean women into sexual servitude for its troops during World War II and agreed to offer 1 billion yen in reparations to the victims through a fund to be created by the South Korean government.

South Korea promised to end the dispute once and for all if Japan fulfills its responsibilities.

The deal came after President Park Geun-hye and Japanese Prime Minister Shinzo Abe held their first-ever one-on-one summit in early November and agreed to accelerate negotiations on the issue in a year marking the 50th anniversary of the establishment of bilateral diplomatic relations.

Historians estimate that more than 200,000 women, mostly Koreans, were forced to work in front-line brothels for Japanese soldiers during the war. Korea was under Japanese colonial rule from 1910 to 1945. The victims are euphemistically called "comfort women." (Yonhap)