Makiko Tanaka, Japan's first female foreign minister, has resigned from parliament two weeks after she gave testimony in an investigation of misuse of public funds.

The move could spell the end of the high-profile, if controversial, political career of Ms Tanaka.

This may well be a strategic move to quit while the atmosphere is bad against her and stand in an election again sometime in the future

Mineaki Yamamoto

Once touted as a possible prime minister, she was sacked as foreign minister in January and suspended from the governing Liberal Democratic Party in June over allegations that she misappropriated government money to pay staff who were not on her official payroll and then failed to co-operate in inquiries.

Ms Tanaka had denied any wrongdoing and has not been charged with any offence.

Commentators are now speculating that the 58-year-old may form her own party or encourage her son to stand for her parliamentary seat to continue the political dynasty started by her father, the late Prime Minister Kakuei Tanaka.

Ms Tanaka was believed to be the most popular member of the Cabinet when Prime Minister Junichiro Koizumi swept to power on the back of reform promises in April last year.

She was credited with playing a key role in Mr Koizumi's rise to prominence and power but fell out with him as a cabinet minister.

High-profile battle

Mr Koizumi sacked Ms Tanaka in January to end her high-profile and disruptive battle with Foreign Ministry officials and Muneo Suzuki, an LDP powerbroker who backed them.

While Ms Tanaka's popularity slumped, so did that of Mr Koizumi.

Political commentator Mineaki Yamamoto said the surprise resignation could be part of a broader strategy to return in better times.

The legacy of Kakuei Tanaka could yet help his daughter

"It's pretty hard to imagine her just going quietly back to an ordinary life," the analyst said.

"This may well be a strategic move to quit while the atmosphere is bad against her and stand in an election again sometime in the future. After all, she still has the legacy of her father's name."

Deputy Chief Cabinet Secretary Kosei Ueno told reporters that Ms Tanaka's resignation was totally unexpected.

"It was a surprise. I think only Ms. Tanaka knows the details," he said, according to public broadcaster NHK television.

Ms Tanaka is the fourth lawmaker to resign from the Japanese parliament this year.