Japan and Russia plan to send a joint research group to the Moscow-held islands at the center of their territorial dispute as early as May 30 with the goal of starting joint economic activities there, diplomatic sources said.

The group — about 50 to 60 people, including government officials and business people — will conduct research for about five days to make a list of potential projects involving the Tokyo-claimed islands off Hokkaido, the sources said Friday.

Prime Minister Shinzo Abe and Russian President Vladimir Putin agreed at their summit in April to send the group over in May. Abe said at the time that conducting joint activities and nurturing mutual trust will help the two countries sign a peace treaty to formally end World War II, which the territorial row has prevented.

Since the group intends to go to the disputed islands by chartered ship, the schedule will be determined by the weather, the sources said.

The two countries need a system for the joint activities that avoids judicial problems because their stances on the sovereignty of the isles remain far apart.

In particular, Japan and Russia have to sort out issues such as jurisdiction when Japanese are involved in accidents or incidents while participating in joint projects, and rules over investment and financing.

Japan has proposed joint economic projects in areas including cultivation of fish and sea urchins, organizing ecotourism services, and building infrastructure for conducting preventive health care using advanced technology, the sources said. Russia is eyeing projects to rebuild old houses on the islands, they said.

The disputed islands of Etorofu, Kunashiri, Shikotan and the Habomai islet group were seized by the Soviet Union soon after Japan's surrender in World War II.