Embryonic stem cells are the source of all tissue. Researchers believe they can be coaxed to grow into heart, brain or nerve cells that could be used to renew ailing organs.

Last year, Hwang's team at Seoul National University created the world's first cloned human embryos. In May, they created the first embryonic stem cells that genetically match injured or sick patients.

The researchers insisted the dog experiment was aimed at creating a reliable research model.

Monkeys are the closest model to humans, and they are crucial to medical research, but Hwang told reporters that cloning a monkey "is technically impossible at the moment."

"Dogs share physiological characteristics with humans," he said. "A lot of diseases that occur in dogs can be directly transferred to humans."

Animal welfare groups criticized the experiment. "This technology could lead to a brave new world of puppy production if it were hijacked by profiteers seeking to use cloning to supply the pet trade," said Wayne Pacelle, president of the Humane Society of the United States.

The researchers nicknamed their canine creation Snuppy, for "Seoul National University puppy," a reference to Hwang's lab. One of the dog's co-creators, Gerald Schatten of the University of Pittsburgh School of Medicine, described Snuppy, now 14 weeks old, as "a frisky, healthy, normal, rambunctious puppy."

On scientific terms, the experiment's success was mixed. Like Dolly, Snuppy was created using a method called somatic cell nuclear transfer.

Scientists took a skin cell from the ear of a 3-year-old male Afghan hound and extracted genetic material from the nucleus. They transferred it to an unfertilized egg whose nucleus was removed. The reconstructed egg holding the DNA from the donor cell was zapped with an electric current to stimulate cell division.

Dog eggs have been problematic because they are released from the ovary at an earlier, less mature stage than in other mammals. This time, the researchers collected more mature eggs from the donors' fallopian tubes.

They implanted 1,095 cloned embryos into 123 dogs and just three pregnancies resulted. That's a cloning efficiency rate lower than experiments with cats and horses. One fetus miscarried and one puppy died of pneumonia 22 days after birth.

That left Snuppy. He was delivered by Caesarean section from his surrogate mother, a yellow Labrador retriever.

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Contributing: Ji-Soo Kim in Seoul