Japanese officials have raided the country's biggest beer makers over allegations they worked together to raise the price of their beverages.

Asahi, Sapporo, Kirin and Suntory Spirits confirmed to the BBC that their premises had been searched by the Japan Fair Trade Commission (JFTC), adding that they would fully cooperate with the regulator.

The four firms dominate Japan's beer market, with their drinks a common sight in supermarkets and convenience stores across the country.

Asahi, Kirin and Sapporo all saw their share price fall after news of the investigation broke on Wednesday. Suntory's beer business is not publicly-listed.

"I do not deny that an investigation is being conducted today, but I'd like to refrain from commenting on the details as a preliminary review is underway," JFTC Secretary General Iwanari Hiroo said, according to local media.

The BBC has contacted the JFTC for comment.

According to the Japan Times, the investigation centres on the companies raising their prices in April last year and in October 2022.

All four companies announced increases, citing the rising cost of raw materials as well as other factors such as energy and transportation.

Kirin Holdings said its subsidiary, Kirin Brewery Company, was searched "on suspicion of a violation of the Antimonopoly Act".

It said it takes the matter "very seriously", adding it would "fully cooperate with the Japan Fair Trade Commission's investigation and any requests for cooperation".

Kirin Holdings said: "At present, the impact of this matter on the company's financial results has not been determined. The company will promptly disclose any material developments as they arise."

A spokesperson for Suntory confirmed "an on-site inspection" had taken place "in connection with a potential violation of Japan's Antimonopoly Act relating to domestic alcohol trade practices".

The company said: "We sincerely apologise for any concern or inconvenience this situation may cause to our customers, business partners, and other stakeholders. We will cooperate fully with the JFTC's investigation."

Asahi said it was "subject to investigation by the Japan Fair Trade Commission" and that it will fully cooperate with the regulator.

It follows an investigation by the regulator in June over alleged cartel activity by some of Japan's biggest ice cream makers, including Meiji and Pocky maker Ezaki Glico.