The surgeons leading the team that separated Ladan and Laleh Bijani yesterday rejected accusations that they acted unethically or unprofessionally in undertaking an operation other specialists had refused to attempt years ago when the risks were smaller.

Dr Benjamin Carson from Johns Hopkins University in Baltimore, said he was struck after meeting the twins last week by their determination to lead separate lives come what may.

"It became very clear in my early deliberations about this situation that they were going to seek separation and continue to do so until it occurred," he said. "The reason that I felt compelled to become involved is because I wanted to make sure they had the best chance.

"Even recognising that the odds were not good, I think it was a worthy humanitarian effort."

The leader of the Singapore team, Dr Keith Goh, said he had tried many times in the past six months to dissuade the sisters from having the operation.

"[But it] was crystal clear that Ladan and Laleh wanted us to go ahead with the separation regardless of the risk because they'd had enough of being stuck together," he said.

Before their operation the sisters, who had studied law at Ladan's insistence, said they wanted to pursue separate careers. Ladan wanted to become a lawyer while Laleh was hoping to become a journalist.

Dr Goh said the final pre-operation tests showed Ladan and Laleh would soon have encountered problems if they had remained conjoined.

Doctors in Germany had rejected the sisters' request for an operation in 1996, claiming the chances of at least one dying were too great. Dr Carson last week rated the chances of success at only 50%.

Dr Richard Nicholson, the editor of Britain's Bulletin of Medical Ethics, told the BBC: "Doctors have a duty to act in the best interests of their patients, and in retrospect one is bound to conclude that maybe this surgery was misguided."