A high-ranking foreign ministry official will become Japan's new top diplomat, after his predecessor resigned over the weekend for accepting illegal political donations, the government announced Wednesday.

State Secretary Takeaki Matsumoto will be promoted to foreign minister later Wednesday, Chief Cabinet Secretary Yukio Edano said. He will replace Seiji Maehara, who stepped down Sunday for receiving political donations from a foreigner, which is prohibited in Japan.

The government moved quickly to replace Maehara, who served in the post for just six months. His sudden resignation was a blow to Prime Minister Naoto Kan's beleaguered government, which is facing public approval ratings below 20 percent.

Kan, who is trying to pass key legislation for his new budget through a gridlocked parliament, had promised to root out "money politics" after a veteran power broker in his party was caught up in a funding scandal.

Matsumoto takes over the post as Japan faces increased aggression from its Asian neighbors. In recent months, Tokyo has had diplomatic spats with both China and Russia over disputed islands in the region, and it faces ongoing threats from nearby North Korea.

Matsumoto is a veteran lawmaker in the ruling Democratic Party of Japan, and served on a number of powerful committees before becoming a No. 2 official at the foreign ministry.

Tsuneo Watanabe, a senior fellow at the Tokyo Foundation think tank, said Tuesday that Matsumoto is an "experienced, mature" diplomat.

Before resigning Sunday, Maehara was seen as a top candidate to replace Kan as prime minister. Kan is already the country's fifth leader in four years, but as his popularity erodes, the ruling Democrats may choose to replace him to stay in power.

Maehara 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.

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.