A senior Democratic Party of Japan member close to Prime Minister Naoto Kan signed a declaration last month that Tokyo should immediately give up its claim to sovereignty over the two South Korea-controlled islets, it was learned Thursday.

Veteran lawmaker Ryuichi Doi resigned as chairman of Lower House Political Ethics Council and as chairman of the DPJ's Standing Officers Council to take responsibility for the incident, dealing another blow to the administration already battered by Seiji Maehara's resignation as foreign minister only days before.

"I never thought it would be this big," Doi, 72, said in a hastily arranged news conference. "I apologize to the people of the nation. I will resign from all the posts in which I am serving."

Doi signed the declaration during a visit to South Korea on Feb. 27 as part of an exchange program between Christian lawmakers. He attended a ceremony to commemorate South Korea's independence movement in 1919 against Japanese colonial rule.

Criticism of Doi, who was born in Seoul during Japan's colonial rule, came from the administration and the ruling bloc, as well as from opposition parties.

"The remark by Doi is regrettable," Kan told the Upper House Budget Committee. "It remains unchanged that the sovereignty of Takeshima belongs to Japan."

"I can't believe (Doi) really said that," a top government official said. Akiko Kamei, policy chief of Kokumin Shinto (People's New Party), whose home district is in Shimane Prefecture, which claims jurisdiction over Takeshima, called Doi's act "extremely deplorable."

Hiroshige Seko of the Liberal Democratic Party said he can't believe a Japanese lawmaker would sign a declaration selling out his own country.

Located in the Sea of Japan, the islets are known as Takeshima in Japan and Dokdo in South Korea.