Due to an oversight, a mailing list set up by the Environment Ministry was publicly accessible until Tuesday, enabling anyone to read internal emails on international negotiations held in January, officials said Wednesday.

All the emails shared by ministry officials on U.S. Internet search giant Google Inc.'s free mailing list were deleted Tuesday night. They had been accessible because the ministry failed to change the service's default settings, the officials said.

It is unclear whether the emails were actually viewed by the public, they added.

The ministry said discussions on the mailing list were no different than the stance taken by the nation at the international conference on a treaty to regulate mercury trading and that Tokyo's position would not have been affected even if the emails had been seen by outsiders.

But the ministry said it was "regrettable" that the emails had been accessible to the public in violation of an internal regulation on information control and that it will "take steps to prevent a recurrence."

At the United Nations talks in January, negotiators agreed on the draft of a new treaty to ban, in principle, the manufacture, export and import of products that contain a certain level of mercury, to help prevent environmental pollution and damage to people's health from the toxic substance.

The pact, to be dubbed the "Minamata Convention" after a mercury-poisoning disease that was officially recognized in the 1950s in Kumamoto Prefecture, will be adopted at an international conference to be held in Japan in October and is expected to take effect around 2018.