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BEIJING - Organ transplants from executed prisoners in China are "quite exceptional", though if criminals want to make such a donation there are no rules against it, Xinhua news agency said.

Some human rights groups have accused Chinese hospitals of turning to lucrative organ sales and transplants to raise funds, and that the source of these human organs can be executed prisoners.

"Actually, the main source of organs for transplant in China is voluntary donation by deceased citizens in accordance with their last wills," Xinhua quoted an unnamed official.

Criminals' organs can only be used if the condemned "have voluntarily expressed the wish to donate their organs and signed relevant documents before death, or their families have given consent to such usage", the report said.

"There is no difference in the procedures of body or organ donation between deceased ordinary citizens and executed criminals," the official said.

If criminals want to donate their organs, then their wishes should be respected "in the interest of mankind", Xinhua added.

Rights groups say an estimated 5000 to 12,000 are put to death in China each year -- more than anywhere else in the world. China does not release any numbers itself.

Xinhua reported the official said Chinese courts have always and would continue to strictly abide by the law concerning the tightly-restricted use of organs of executed criminals, and effectively safeguard the rights and interests of prisoners subject to the death penalty.

Since July, the sale of human organs in China has been banned. Hospitals now require written consent of donors and restrict the number of hospitals allowed to perform transplant operations.

There are about two million people in China who need transplants each year, but only around 20,000 operations are carried out because of shortages, state media has said.