The operator of the crippled Fukushima Daiichi nuclear power plant says it detected tritium in seawater off the plant, but that the concentration of the element stays very low and poses no safety problem.

Tokyo Electric Power Company has been taking samples from the sea within 3 kilometers of the plant daily to check and publish tritium levels since it started the treated and diluted water discharge on August 24.

It has set 10 becquerels per liter as the minimum level detectable for daily rapid analysis.

The first detection since of tritium was from one of Thursday's samples. The utility says the concentration of tritium was 10 becquerels per liter -- the minimum detectable level.

TEPCO said the sample was taken from about 200 meters north of the water discharge outlet. The location is the closest one to the outlet among TEPCO's ten monitoring points.

The utility said the tritium concentrations were below the minimum detectable level at other nine locations.

TEPCO also released the results of an analysis done with a lowered minimum detectable level on the sample from the day of the start of the discharge.

It said the analysis showed that a tritium concentration in the sample taken from the point similarly about 200 meters north of the outlet measured 2.6 becquerels per liter.

TEPCO sets 700 becquerels per liter as the level to stop the discharge. It said there is no safety issue in the discharge, and the release has been done as planned.

Separately, Japan's Environment Ministry announced that its latest weekly test results of water samples from 11 points around the discharge outlet showed the tritium levels were below the minimum10 becquerels per liter at all points.