TOKYO -- Tokyo Electric Power Company Holdings (TEPCO) announced Monday that it decided to postpone the restart of the No 6 reactor at its Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture.

An alarm system for the control rods, which are used to suppress the nuclear fission reaction, failed to sound during a test operation held on Saturday, TEPCO said.

The restart of the No 6 reactor at the seven-unit complex was originally scheduled for Tuesday.

The Kashiwazaki-Kariwa plant, about 220 km northwest of Tokyo, was among 54 reactors shut following the March 2011 core meltdowns at TEPCO's tsunami-stricken Fukushima Daiichi plant. The Niigata Prefectural Assembly approved in December the partial restart of the plant amid criticism.