The government plans to submit a proposal to UNESCO by around the end of the month to add a number of islands in the country's southwest to the natural sites on the World Heritage list, the government's top spokesman said Wednesday.

It is also expected to propose that a number of sites in Nagasaki and Kumamoto prefectures linked to the history of Japan's persecuted Christians be added to the cultural sites on the World Heritage list.

The natural sites include land on the northern part of the main island of Okinawa Prefecture returned to Japan last month after being used as a U.S. military training area, Chief Cabinet Secretary Yoshihide Suga told a news conference.