Major Japanese mobile carrier KDDI says it has mostly restored services following a nationwide network disruption over the weekend. The company says services won't be fully restored until Tuesday evening at the earliest.

KDDI Senior Managing Executive Officer Yoshimura Kazuyuki said the company sincerely apologizes to its customers for the trouble.

The company said the recovery work was slowed by heavy traffic concentrated on some network equipment.

Nearly 40 million customers across Japan were unable to make voice calls or access the internet when the network was disrupted on Saturday.

Connection issues also plagued customers of KDDI's other brands, UQ mobile and povo.

The disruption had a major impact on a wide range of businesses, including those in the medical and transportation sectors and weather tracking services.