Russian Foreign Minister Sergei Lavrov shakes hands with his Japanese counterpart Taro Kono after a news conference in Moscow, Russia May 10, 2019. (REUTERS)

MOSCOW, May 10 (Xinhua) -- It won't be easy for Russia and Japan to reach an agreement on a post-World War II peace treaty, Russian Foreign Minister Sergei Lavrov said here Friday following talks with his Japanese counterpart Taro Kono.

"The issue can be solved only through long, painstaking and creative work," Lavrov told reporters.

The only way to signing a peace treaty is to "improve Russian-Japanese relations to a qualitatively new level" through the comprehensive development of bilateral ties, he said.

Lavrov announced that the fourth round of negotiations of foreign and defense ministers in the so-called 2+2 format will be held in Tokyo on May 30.

Moscow and Tokyo have failed to sign a postwar peace treaty due to their rival claims to four Pacific islands, called Southern Kuril Islands in Russia and Northern Territories in Japan.

The two countries are currently holding consultations on joint economic activities on the islands in five areas, namely aquaculture, greenhouses, tourism, wind energy, and waste recycling. They view the cooperation as a step toward a peace treaty.

Lavrov said that he and Kono "agreed to focus on specifying cooperation projects, which are at an advanced stage of coordination, in order to develop appropriate business models."

Kono said that he and Lavrov failed to overcome differences on the peace treaty issue during Friday's frank discussion.