Tokyo police took the unusual step of arresting the leader of a fringe political group and two associates on Friday for allegedly obstructing campaigning of competing candidates in the lead-up to a Diet by-election in April, investigative sources said.

Atsuhiko Kurokawa, 45, leader of the Tokyo-based group "Tsubasa no To," Ryosuke Nemoto, 29, its unsuccessful candidate in the April 28 House of Representatives by-election, and a supporter, Hayato Sugita, 39, who was helping on the campaign, were arrested after being accused of disrupting rivals' campaigning activities with loudspeakers, they said.

(From L) File photo shows Hayato Sugita, Atsuhiko Kurokawa and Ryosuke Nemoto talking to reporters in Tokyo on May 13, 2024, four days before they are arrested for allegedly obstructing campaigning of competing candidates in the lead-up to a by-election in April. (Kyodo)

After receiving complaints from several parties, the police searched the Tokyo office of the group and the houses of Kurokawa and Nemoto, who serves as the group's secretary general, earlier this week.

When campaigning for the by-election officially kicked off on April 16, Kurokawa was seen climbing atop a telephone box to use a loudspeaker, almost completely drowning out a speech by rival candidate, independent Hirotada Ototake.

The police warned the trio two days later that their loud speeches and blasting of car horns near where Ototake was campaigning in front of Kameido Station in Tokyo violated the public offices election law, but they continued doing so, the sources said.

In a file photo taken on April 16, 2024, Atsuhiko Kurokawa (lower R), head of the political group "Tsubasa no To," speaks near where candidate Hirotada Ototake (upper L) is holding a stump event in Tokyo's Koto Ward ahead of the April 28 House of Representatives by-election. (Kyodo) ==Kyodo
Investigators from the Metropolitan Police Department carry items from a building housing the office of the political group "Tsubasa no To" on May 13, 2024, in Tokyo, following a search related to campaign obstruction in the April 28 House of Representatives by-election, in a rare move after receiving complaints from several other camps in the race. (Kyodo) ==Kyodo

In the race involving nine candidates, 37-year-old Natsumi Sakai, backed by the Constitutional Democratic Party of Japan, sealed victory with 49,476 votes, while Nemoto placed last with 1,110 votes.

Tsubasa no To campaigns on policies opposing the consumption tax and globalism among other fringe issues.

Kurokawa posted video footage on his YouTube channel, which has 250,000 subscribers, of the activities that drew complaints. He has said he plans to run in the Tokyo gubernatorial election on July 7.

Under the law, those who obstruct speeches or rallies of candidates in an election campaign could face imprisonment for up to four years or a fine of up to 1 million yen ($6,400).