South Korea has denied entry to the leader of the Raelian sect which runs Clonaid, a company that claims to have created the first human clone.
Claude Vorilhon, known as Rael, was forced to leave South Korea after being detained for nine hours at Incheon International Airport, the justice ministry said.
Rael had arrived in Seoul aboard a Korean Air flight from Toronto for a 17 day stay that would have included a series of public lectures on human cloning, it said.
"We banned him because his presence may hurt our national interests or cause social disorder,"" a ministry official told AFP.
Clonaid, based in Las Vegas, Nevada, was founded in 1997 by the Raelians, who claim 60,000 followers worldwide, 4,000 of them in South Korea
Raelians believe cloning is the key to eternal life, allowing human consciousness to be passed into successive bodies.
Prosecutors have investigated Clonaid's South Korean subsidiary over its claim that South Korean women had been involved in a human cloning experiments.
The Raelians believe life on Earth was established by extra-terrestrials who arrived in flying saucers 25,000 years ago and cloned humans.
In a statement, the Raelian movement said their leader was not in charge of cloning activities run by Clonaid, and described the decision to deport him as discrimination against religious minorities.
Clonaid claimed the birth of the first human clone on December 26, a claim that has still not been proven. Many scientists remain sceptical.