Yoshitaka Ikeda, 57, a lower house lawmaker and former vice minister for education, was arrested by Tokyo prosecutors, Kishida told reporters, adding that Ikeda would be expelled from the Liberal Democratic Party (LDP).

"This is very regrettable. I take it very seriously," Kishida said in broadcast remarks. "As a party, we must work to restore trust in politics with a strong sense of urgency."

Ikeda allegedly received a kickback of some 48 million yen ($330,000), the largest among the LDP faction of the late former Prime Minister Shinzo Abe, which is at the centre of the biggest fundraising scandal to engulf the ruling party in decades, public broadcaster NHK said.

An official with the prosecutors office said he could not discuss the case over the phone. The office has previously told Reuters it could not comment on any ongoing investigation.

No one responded to calls to Ikeda's offices in Tokyo and his base in central Japan. Footage on NHK showed a sign on the door of Ikeda's offices saying they were temporarily closed.

The scandal last month forced the resignations of Abe faction heavyweights Hirokazu Matsuno as Kishida's chief cabinet secretary, Yasutoshi Nishimura as trade and industry minister and Koichi Hagiuda as LDP policy chief.

The three have not commented on media reports about their involvement.

Prosecutors suspect the Abe faction failed to report as much as 500 million yen ($3.5 million) in funds over five years, while the LDP's smaller Nikai faction was believed to have not reported 100 million yen, NHK has said.

Media reports have said prosecutors were examining whether other LDP factions, including the one Kishida previously headed, were involved in the scandal.

Kishida's support had sunk to around 20% in mid-December in newspaper public opinion surveys, the lowest for any prime minister in more than a decade.

The investigation centres on money raised from ticket sales to party events, some of which was allegedly given directly to lawmakers by the party and left off the books, despite requirements to report such payments under the Political Funds Control Act.

($1 = 144.6500 yen)

(Reporting by Kevin Buckland; Additional reporting by Nobuhiro Kubo; Editing by William Mallard)

By Kevin Buckland