Japanese opposition parties on Sunday piled pressure on the centre-left government with calls for Foreign Minister Seiji Maehara to resign over a fresh donation scandal.
Less than a year after taking office, beleaguered Prime Minister Naoto Kan is already struggling with public approval ratings below 20% and the threat of legislative gridlock from the opposition.
Now in a fresh blow to his ruling Democratic Party, it emerged Friday that Maehara -- largely seen as a potential successor to the unpopular Kan -- had received a donations from a foreign resident of Japan, in violation of the law.
Maehara immediately apologised for having taken at least 50,000 yen ($610) from the woman, a Korean descendent, whom he said he has known since childhood.
Japan, which occupied the Korean peninsula until the end of World War II, is home to nearly one million ethnic Koreans, many of whom are children of former forced labourers and do not hold Japanese nationality, despite having lived their entire lives in the country.
Maehara said he had not been aware of the donation until last week, but opposition parties have gone on the offensive, saying the violation of the law should be taken seriously and calling for his resignation.
"He should take responsibility over this issue," said Hirofumi Nakasone, the upper house chairman of the opposition Liberal Democratic Party, during a Sunday debate show on public broadcaster NHK.
"Mr. Maehara is the country's minister in charge of diplomatic affairs... We will continue to press for him to take responsibility."
Kazuyoshi Shirahama of the New Komeito said: "When you think of his position as foreign minister, we must think about the impact of this on diplomatic matters."
"I believe he should step down," he said.
Maehara on Saturday said he would not be resigning.
"I would like to continue working and overcome this difficult time," he told a press conference. "This matter has never affected the nation's diplomatic policies, and it's impossible that it will."
Kan told reporters Friday that the case will be investigated thoroughly.
The troubled premier also faces a party revolt, with 16 of his own lawmakers, who are close to his inner party nemesis and faction boss Ichiro Ozawa, boycotting the vote for his government's record $1.1-trillion budget last week.