TOKYO - Japan's nuclear safety agency detected elevated levels of radiation inside the buildings housing the No 1 and No 3 reactors at the troubled Fukushima No 1 nuclear power plant, local media reported Monday.

The readings were between 10 and 49 millisieverts per hour for the No 1 unit and between 28 and 57 millisieverts per hour for the No 3 unit.

The Nuclear and Industrial Safety Agency said that the readings put time constraints on any work that must be done inside the reactors, according to Kyodo News report.

On Sunday, two remotely controlled robots were sent to measure radiation levels and other parameters inside the buildings.

Tokyo Electric Power Co (TEPCO), operator of the Fukushima nuclear plant said Sunday that the crippled plant will be stabilized to a condition known as "cold shutdown" in about six to nine months.