"I'm very concerned about cloning," the president told reporters in the Oval Office during a photo opportunity with the prime minister of Denmark. "I worry about a world in which cloning becomes accepted."
He also expressed concern about human.
White House deputy press secretary Trent Duffy said the work in South Korea amounted to human cloning for the sole purpose of scientific research. "The president is opposed to that," Duffy said. "That represents exactly what we're opposed to."
Mr. Bush, in his fifth year in office, has not yet exercised his first veto. The White House also promised a veto this week of a highway bill if it exceeded the administration's spending limits.
A measure by Reps. Mike Castle, R-Del., and Diana DeGette, D-Colo., would lift Mr. Bush's 2001 ban on the use of federal dollars for research using any new embryonic stem cell lines. The president said he would veto such a measure if it reached his desk.
"I made very clear to Congress that the use of federal money, taxpayer's money, to promote science which destroys life in order to save life – I'm against that," he said. "Therefore, if the bill does that, I would veto it."
The stem cell debate has split Republicans in Congress.
House Speaker Dennis Hastert, R-Ill., had agreed to allow a vote on the Castle-DeGette bill, but after Castle and other moderate Republicans angered conservatives by sponsoring polls in their districts on the issue, Hastert and Majority Leader Tom DeLay, R-Texas, said they would pair the bill with a separate measure to encourage umbilical cord stem cell research.
DeGette on Thursday said the GOP leaders' plan was "a weak attempt to divert support from our bill."
"The bills are completely compatible," she said. She said she intends to vote for both measures and will encourage other members to do the same.