TOKYO (Kyodo) -- Suspended coupled bullet train services in northeastern Japan will gradually resume later this week, the operator said Tuesday, after safety concerns arose when linked trains decoupled in motion on the Tohoku Shinkansen line for the second time in less than six months.

JR East said services will restart Friday in stages after securing couplers with metal fittings to prevent disconnections, with full operations resuming Saturday. The railway company is the only operator that links shinkansen trains of different compositions.

The incident took place last Thursday on a service connecting two high-speed trains on the shinkansen line linking Tokyo and stations in northeastern Japan. JR East experienced a similar occurrence in September 2024.

No one was injured in the latest incident, but the operator said its investigation found that the coupler had repeatedly gone through a separation process. JR East said it will continue its probe, suspecting an electrical malfunction.

After the incident, the firm said all coupled bullet train operations would remain suspended until the cause is determined. Last year's case was the first-ever instance of linked shinkansen trains decoupling while in motion.