Japan's main ruling Liberal Democratic Party has won four out of five parliamentary by-elections, increasing its Diet presence by one seat from its pre-election standing.

LDP candidates prevailed in three single-seat constituencies for the Lower House -- one in Chiba Prefecture and the other two in Yamaguchi Prefecture.

One of the Yamaguchi districts was an electoral base for former Prime Minister Abe Shinzo, who was fatally shot last July.

Another LDP candidate secured an Upper House seat in Oita Prefecture, edging past the only other contestant by a mere 341 votes.

LDP Secretary-General Motegi Toshimitsu welcomed the results. He said voters gave a positive interim evaluation for the administration of Prime Minister Kishida Fumio.

The Nippon Ishin Japan Innovation Party won a Lower House by-election in Wakayama Prefecture, marking its first victory in a single-seat constituency there.

The head of the party, Baba Nobuyuki, said the outcome will greatly help it boost its showing in the western region of Kansai and other areas nationwide. Kansai consists of Osaka and surrounding prefectures.

The largest opposition Constitutional Democratic Party failed to win a seat this time. CDP Secretary-General Okada Katsuya said the results are very regrettable. He said his party will work to produce a good outcome in the next general election.

The by-elections coincided with the second half of unified local elections. Voting took place for 679 mayoral and municipal assembly contests. This excludes 233 elections whose results were decided without votes.

A newcomer supported by the LDP and Komeito clinched the mayoral post in the city of Nagasaki.