Pope John Paul has condemned human cloning as an arrogant attempt to improve on God's creation.
"The sense of power that every technical progress inspires in man is well known," the pope said in a message sent from his summer residence in Castelgandolfo to a meeting of prominent Catholic cultural, political and business leaders in the Italian city of Rimini.
"The attempt by man to appropriate the source of life by experimenting with human cloning is example enough," he said in a message sent at the start of the week-long event.
The comments come less than two weeks after British scientists were given permission to clone human embryos for medical research - believed to be the first such licence granted in Europe.
The pope said medical research should not try to "manipulate" human beings "according to a project considered with arrogance better than that of the Creator himself."
"The way taught by Christ is another: it is that of respect for human beings," he said, urging ethically responsible science.
The Vatican has repeatedly condemned all attempts at human cloning, comparing it to the experiments carried out by Nazis in World War Two.