Mitsubishi Tokyo Financial Group Inc. and UFJ Holdings Inc. formally announced Friday the postponement of the planned integration of their core banking units until Jan. 1, three months after their original schedule.

The closely watched merger of the two financial groups would create the world's biggest financial entity, with total assets worth 190 trillion yen.

The reason for the delay is that the two banks -- Bank of Tokyo-Mitsubishi and UFJ Bank -- want to spend more time to ensure there will be no problems when they combine their banking operations, including computer systems, the banks said.