U.S. government officials have offered condolences to the family of Shigeru Yokota, father of a girl abducted by North Korea in the 1970s, after his death last week, the family said Thursday.

Shigeru, who died Friday at age 87, and his wife Sakie had long lobbied the United States for support in their efforts to secure the return of their daughter Megumi who was taken to North Korea at age 13 in 1977.

Deputy U.S. Secretary of State Stephen Biegun sent a letter to Shigeru's son Takuya, 51, saying he was "particularly moved by (Shigeru's) untiring efforts to raise international awareness of the abduction issue as one facet of North Korea's abysmal human rights record."

(U.S. Special Representative for North Korea Stephen Biegun speaks to reporters after arriving in Beijing on Dec. 19, 2019)

"The United States will continue to seek resolution of the abductee issue in our efforts on North Korea and continue to advance your family's important work," Biegun said.

In another letter addressed to Sakie, 84, Joseph Young, charge d'affaires ad interim at the U.S. Embassy in Tokyo, wrote, "Your husband's strength and conviction regarding Megumi-san and the cause of the other abductees were truly inspiring to so many people in the United States and around the world."

"Please know that our entire U.S. Mission to Japan joins you and your family in mourning," Young said. "We will continue to work with even greater fervor on behalf of Megumi-san and the other abductees so as to honor Mr. Yokota's legacy."

(File photo taken in November 2017 in Kawasaki, near Tokyo, shows Shigeru Yokota (R) and his wife Sakie, the parents of Megumi Yokota, a symbolic figure in the issue of North Korea's abductions of Japanese nationals in the 1970s and 1980s. Shigeru Yokota died on June 5, 2020, at age 87)

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The Yokota family, also including Tetsuya, Takuya's twin brother, said in a statement they will "continue their battle until they are reunited with Megumi, and continuous U.S. support would be greatly appreciated."

Shigeru worked for more than two decades with family members of other abduction victims in pressing the Japanese government to rescue their children and siblings, whom they believe are still alive in the North.

He served as head of the group for more than 10 years until November 2007. The Yokotas advocated on behalf of other Japanese nationals abducted in the 1970s and 1980s.

Their efforts were brought to the attention of U.S. President Donald Trump and he referred to Megumi in an address to the U.N. General Assembly in September 2017.

Japan officially lists 17 citizens as abduction victims and suspects North Korea's involvement in many more disappearances.

While five of the 17 were repatriated in 2002, Pyongyang maintains that eight, including Megumi, have died and the other four never entered the country.