A grandson of physicist Robert Oppenheimer, who led nuclear bomb development by the United States during World War Two, has urged Japan to make efforts for global cooperation.

Charles Oppenheimer held a news conference at the Japan National Press Club in Tokyo on Monday. He came to Japan in late May.

He has been working on a project in the US to pursue nuclear non-proliferation and address climate change.

His grandfather is said to have opposed the development of hydrogen bomb and nuclear proliferation after learning about the horrors of the atomic bombings in Japan.

Speaking to reporters, Oppenheimer urged people to listen to his grandfather's call for global unity and think about world peace, as tensions between super powers are escalating and the arms race continues.

He said it seems the world is entering a newer phase of more danger than ever before and escalating tensions between the US, China and Russia is the biggest danger in the world if they can't increase communication at least and cooperation between those countries.

He added that he believes Japan is probably in the best place in the world to call for more cooperation between these powers.

He also said he has met with atomic bomb survivors, or hibakusha, in Hiroshima during his visit and heard their stories.

He stressed that he believes all bombs are immoral, not just atomic bombs, and they should never be used by humanity.