TOKYO — Japanese diplomacy won't be affected by the overnight resignation of the country's foreign minister for accepting an illegal political donation from a foreigner, Japan's embattled prime minister said Monday.

The resignation of Foreign Minister Seiji Maehara Sunday night is a blow to Prime Minister Naoto Kan's already shaky government. It also highlights the high turnover rate that has plagued government officials in recent years and is likely to further erode public confidence in Kan, whose public approval rating has fallen below 20 percent.

Kan is the country's fifth leader in four years, and the 48-year-old Maehara had been seen as a leading candidate to replace him if it was decided a change was the best way to keep their ruling Democratic Party of Japan in power.

Chief Cabinet Secretary Yukio Edano will temporarily double as foreign minister, and Kan said the change would not affect the country's international relations.

"Diplomacy is extremely important. We will remain firm," Kan said during a parliamentary session Monday.

The change comes as Japan, a key U.S. ally in the Pacific, grows increasingly wary of China's increased assertiveness in the region, highlighted by a territorial spat last fall over disputed islands that both countries claim. Japan also faces threats from nearby North Korea.

Maehara, who was foreign minister for just six months, acknowledged receiving a total of 250,000 yen ($3,000) over the past several years from a 72-year-old Korean woman who has lived most of her life in Japan. He said they had been friends since his childhood.

An opposition politician raised the allegation late last week and Maehara stepped down late Sunday. Japanese law prohibits lawmakers from accepting donations from any foreigners, even those born in Japan.

It very hard for foreigners to become Japanese citizens, even if their families have lived in the country for generations. Hundreds of thousands of ethnic Koreans, many descended from laborers brought forcibly to Japan during World War II, live in the country legally but without citizenship.

Maehara's admission undermines Kan's pledge to root out "money politics" after a veteran power broker in their party, Ichiro Ozawa, was ensnared in a political funding scandal. Ozawa says he is innocent, but the party has recommended revoking his membership.

"I apologize to the people that I ended up resigning after just six months on the job, and for causing distrust due to a politics-and-money problem despite my pledge to seek clean politics," Maehara said Sunday during a televised news conference. "It's truly regrettable that I caused such a problem because of my own mistake."

Opposition parties, which have worked hard to obstruct the Democrats' attempts to pass the budget and move ahead on other legislation, will likely be emboldened by Maehara's resignation.

The gridlock in Japan's parliament has caused many Japanese to become disillusioned with the government's inability to tackle serious problems, from a lackluster economy and bulging national debt to an aging, shrinking population.

Atsuo Ito, an independent political analyst, said the resignation was inevitable to save Kan's government from further trouble.

"If he had stayed on, he would have come under heavy fire in parliament," he said in an interview with Fuji TV.