An anonymous sender earlier this month mailed a package to the Environment Ministry apparently containing dirt contaminated by radioactive fallout from the Fukushima No. 1 nuclear plant that was later dumped in an empty lot near a ministry official's home in Saitama Prefecture, Environment Minister Goshi Hosono revealed Thursday.

The ministry received another box Wednesday, apparently from the same sender.

Hosono apologized to the public at a news conference and said the officials involved in discarding the soil would be punished. The names of the officials were not released.

According to the ministry, the small box with the soil was delivered Nov. 8, sent by someone claiming to reside in the city of Fukushima.

A message written on the top of the box instructed the ministry to dispose of the soil, which allegedly came from the sender's property.

From a distance of about 0.8 meter from the box, radiation measured 0.18 microsievert per hour.

The head of the ministry's general affairs section determined that the contamination didn't exceed levels that had been found in other parts of the Kanto region and therefore was not a threat.

In a meeting with other ministry officials, it was decided that one of them would take the soil home and dump it, which was done Sunday.

"This incident should not have happened," Hosono said. "This is a problem for the organization (of the ministry), rather than one for individual officials."

Hosono concurrently serves as minister in charge of dealing with the Fukushima nuclear accident.

The ministry retrieved the soil Thursday.

The other small box apparently sent from the same person that arrived Wednesday remained unopened Thursday.