The Justice Ministry revealed Friday that at least four construction companies have used foreign trainees in radioactive cleanup work related to the triple meltdown at the Fukushima No. 1 nuclear power plant, which occurred in 2011.

The interim report of the ministry's probe, covering 182 companies with foreign trainee programs as of June 29, said one of the four companies, based in Iwate Prefecture, has been banned from accepting foreign trainees for five years.

The other three firms — two in Fukushima Prefecture and one in Chiba Prefecture — are still under investigation. The names of the companies were not revealed.