Cloning pioneer Hwang Woo-suk has called "extraordinary" the Harvard Medical School breakthrough of creating stem cells without destroying embryos.

Hwang on Tuesday said the achievement will complement his own team's research as the Harvard group will conduct joint research with him on finding a cure for diabetes.

Scientists at Harvard on Monday announced the creation of a new kind of hybrid stem cell by fusing adult skin cells with embryonic stem cells, opening the prospect of creating stem cells without destroying cloned, early-stage embryos.

Hwang, however, called for further studies to prevent rejection when replacement parts to be grown from the hybrid stem cell are transplanted onto a person.

Hwang said the new technique runs the risk of immune rejection since the hybrid cell contains the DNA of the person who donated the skin cell and the DNA in the initial embryonic stem cell.