KDDI Corp. said Monday its "au" mobile phone services experienced technical difficulties across Japan, causing disruptions to calls and internet connections for about three hours.

The service disruption, which began at 7:18 a.m., initially affected 31 prefectures in western Japan, including Osaka, Kyoto and Fukuoka, before extending across the country.

The services returned to normal around 10:11 a.m., according to KDDI, one of Japan's three major telecommunications carriers.

The company said some services, particularly data communication, were impacted nationwide. The cause of the outage remains under investigation.

The trouble affected emergency calls as well as services offered under the company's budget brands. Some mobile service operators that rent KDDI's networks experienced a similar problem, the company said.

The disruption came after the company experienced a massive service outage in July last year, which lasted for about 61 hours.

KDDI "deeply apologizes for the trouble it caused to our customers," it said in a statement.

Japan's top spokesman Hirokazu Matsuno told a press conference, "It is extremely regrettable as (KDDI's) infrastructure is important for people's daily lives and economic activities."

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