Japanese Prime Minister Fumio Kishida said Monday he is not thinking about dissolving the lower house and calling a snap election, a day after his Liberal Democratic Party won parliamentary by-elections in four of five seats.

"As we have to carry out important policies one by one, I am not thinking of (a lower house) dissolution and a general election for the moment," Kishida told reporters at the prime minister's office.

Prime Minister Fumio Kishida speaks to reporters at his office in Tokyo on April 24, 2023. (Kyodo)

There has been speculation Kishida may have been planning to call an election after the Group of Seven summit in Hiroshima next month amid improvement in approval ratings for his Cabinet.

Kishida pledged to "press on with my work in running the government with the public's voice in mind."

Key challenges for Kishida's government include a falling birth rate, which threatens the country's economic and social sustainability.

The number of babies born in Japan last year fell to below 800,000 for the first time since record-keeping began in 1899, official data showed.

In the five by-elections on Sunday, the LDP won four of them -- the Chiba No. 5 district, the Yamaguchi Nos. 2 and 4 districts in the House of Representatives, and the Oita prefectural district in the House of Councillors.

The LDP candidate was defeated in the Wakayama No. 1 district in the lower house by a new face backed by the Japan Innovation Party, which has a strong foothold in the Kansai region in western Japan.

Meanwhile, the main opposition Constitutional Democratic Party of Japan lost some close races.

Under the Constitution, a prime minister has the final say on the dissolution of the lower house for a snap election. The current four-year terms for lower house members expire in October 2025 unless Kishida dissolves the chamber.

Kishida took office in October 2021. The next LDP presidential race is slated to be held in September 2024.

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LDP wins 4 of 5 Diet by-elections amid snap election speculation