Ladan and Laleh Bijani, 29-year-old Iranian joined twins died during the Operation to Separate them

They wanted to see each other face to face, they said, and to pursue independent lives. And so Ladan and Laleh Bijani, 29-year-old Iranian twins who were born joined at the head, asked doctors to go ahead with a risky operation to separate them.

Neither survived. The sisters died of blood loss yesterday afternoon within 90 minutes of each other, doctors said, after a team of surgeons at Raffles Hospital in Singapore worked for 50 hours to separate their brains.

The operation was the first known attempt to separate adult twins joined at the head.

''When we undertook this challenge, we knew the risks were great,'' Dr. Loo Choon Yong, the hospital's chairman, told reporters at a news conference.

The Bijani sisters had captured the attention and hopes of much of Singapore, which is still recovering from its battle against severe acute respiratory syndrome, the pneumonia-like disease that killed 32 people here. News of the twins' deaths brought tears to the many well-wishers who had gathered for a prayer vigil outside the hospital since the operation began on Sunday.

People also wept publicly across Iran when state-run television announced the Bijanis' deaths. The sisters, who had trained as lawyers, were celebrities there, and President Mohammad Khatami had sent them a message and prayed for their well-being before the operation.

The case raised ethical questions within Singapore's medical community about whether doctors should allow patients to undergo such risky procedures. But the twins had asked doctors to go ahead with the operation even after being warned that there was at least a 50 percent chance that one or both would die or suffer severe brain damage.

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Alireza Safaian, the twins' adoptive father, said he knew from the moment he heard about the surgery that both sisters would die.

''I was sure they would die and I told everyone about this but the media did not pay attention to what we were saying,'' he said.

He said he had taken the sisters to Germany when they were 2, and doctors said that one of them would die if surgeons tried to separate them. He sought advice from Ayatollah Ruhollah Khomeini, who was in exile in Najaf.

''He was not a doctor but was close to God,'' Mr. Safaian said. Ayatollah Khomeini said the surgery was not religiously permissible and would be considered murder since doctors knew in advance that one twin might die.

Mr. Safaian and his son and daughter, who grew up with the sisters, wept yesterday as they watched an old videotape of Ladan and Laleh at the welfare institute in Tehran where Mr. Safaian works. Mr. Safaian said the twins had led normal lives before the surgery. They lived alone for the past two years, did their own shopping and cooked for as many as 20 guests, he said.

''They were victims of a big propaganda in Iran and Singapore,'' Mr. Safaian said. ''They were used as laboratory mice. I read about the surgery three months ago but the ones who convinced them to go through with it did not let them come see us. Now my girls are gone and there is nothing I can do to bring them back.''

The twins' biological father, Dadollah Bijani of Firouzabad village in southern Iran, told an Iranian newspaper that he had tried to talk them out of the surgery but that their minds were made up.

Similar operations have been reported on 30 to 40 sets of infants and young children since the 1920's, but the death rate has been high, about 50 percent, and many survivors have suffered brain damage.

Guatemalan twins, now 2 years old, who were separated last August by surgeons at the University of California at Los Angeles, still require physical and occupational therapy, and one suffered a neurological setback after contracting meningitis after returning to Guatemala, said a spokeswoman for the hospital. Doctors at Medical City Hospital in Dallas are now making plans to separate 2-year-old brothers from Egypt.

In 2001, doctors in Singapore succeeded in separating twin infants born in Nepal. That operation helped put Singapore -- and the neurosurgeon who led it, Dr. Keith Goh -- on the map of cutting-edge medical centers.

Complicating the Bijani sisters' case was the fact that their brains had grown closely intertwined over the years and shared a major vein. In 1996, German doctors again turned down their request for an operation, saying the shared vein made surgery too dangerous.

Before the operation, Raffles Hospital convened an ethics committee and decided to proceed after determining that the twins were still willing even after being made aware of the risks involved. In addition to physiotherapy sessions to prepare them for their surgical ordeal, the Bijanis met with counselors and psychologists to prepare them mentally.

Dr. Goh assembled a team of 100 medical professionals and more than a dozen doctors from several countries, including a noted American expert on such operations, Dr. Benjamin S. Carson, director of pediatric neurosurgery at Johns Hopkins Children's Center. Speaking at a news conference after the twins' death, Dr. Carson said: ''The women certainly understood the risks and were determined to proceed. I felt compelled to get involved to help give them their best chance at survival and separation, and I have no regrets over my decision. No act is a failure if you learn from it.''

With the sisters' brains sharing a major vein, surgeons fashioned a duplicate vein from a graft taken from Ladan's right thigh.

According to a hospital press release, separation of the twins' brains had reached an ''advanced stage'' by 1:20 p.m. But as the surgeons toiled to separate the many tiny blood vessels connecting the sisters' brains, the twins began to lose blood pressure. Ladan died at 2:30 p.m. At 4 p.m., Laleh was pronounced dead.

At their news conference in June, the Bijanis explained how, despite having lived every moment of their lives together, they had developed divergent interests. Laleh liked computer games, newspapers and books. Ladan liked to chat on the Internet, read the Koran and pray. The sisters hoped to pursue individual careers. While Ladan said she planned to continue in law, Laleh said she hoped to become a journalist.

But one desire remained foremost, they told reporters. ''We want to see each other -- face to face,'' said Laleh. ''We want to see each other,'' Ladan added, ''without a mirror.''

Chart/Diagram: ''Surgery to Separate Conjoined Twins'' Adult Iranian sisters, 29, joined at the head, died from blood loss during the final stages of an operation to separate them. Diagram highlights the vein sisters Laleh and Ladan shared between two brains. The twins had separate brains, but shared a vein to the heart. Laleh kept the original vein. Ladan received a new vein from her thigh. (Sources: Raffles Hospital, Singapore; Johns Hopkins Medical Institutions; Associated Press)