Japan won't grant visas to most members of a group of Nigerian doctors planning to attend a conference in Hiroshima sponsored by the International Physicians for the Prevention of Nuclear War, its U.S. affiliate said Wednesday.

The Foreign Ministry said it rejected requests from nine of the 13 Nigerian applicants. Kazuo Inamura, a senior official in the Foreign Nationals' Affairs Division, said the ministry "does not explain individual reasons for rejection (of visas)."

The Nigerian doctors planned to attend the three-day confab that starts Friday to discuss and learn about nuclear issues and the health effects of radiation exposure, according to Physicians for Social Responsibility, an affiliate of the IPPNW, which won the Nobel Peace Prize in 1985.

Jeff Paterson, the incoming president of Physicians for Social Responsibility, said he is "very disturbed" by the Japanese government's decision and is seeking an explanation.

Among the nine doctors refused a visa is Ogebe Onazi, a member of the IPPNW board of directors who participated in the Arms Trade Treaty talks in New York in July. None of the 13 Nigerians has a criminal record, Onazi said.