RIYADH, 18 September — A complex surgery to separate Malaysian Siamese twins conjoined at the stomach was being performed at King Abdul Aziz Medical City here yesterday.

A total of 41 doctors, nurses and paramedical staff were taking part in the operation, which was expected to take more than 15 hours.

A website of the hospital said the operation was progressing well. It began at 9.45 hours but the preparation started at 7.00 hours, the website said. At 7.30 the twins were put on sedation. By 15:00 hours, doctors finished abdominal adhesions and division.

The pediatric orthopedic surgeon split the symphysis pubis bone, ready for the pediatric urologist to start re-implantation of ureters.

“By 18:00 hours, the surgeons completed angio chest wall separation,” the website said. “Pediatric orthopedic surgeon will soon start to separate illiac wing. Soon after the patient will be turned over,” the website said.

At 20:00 hours doctors were checking position of blood vessels in the illiac wing with x-rays, before separating.

Dr. Abdullah Al-Rabeea, deputy executive director of health affairs at the National Guard, said that the operation would take at least 15 hours.

After the operation the twins will remain in the intensive care unit for about two weeks and under observation for about two to three months.

Rabeea and the hospital’s doctors said the twins would be able to lead a normal life after a successful operation, which is to cost about SR1.5 million.

The medical city has already successfully separated two sets of conjoined twins.

The twins, named Ahmad and Mohammed Rahman, accompanied by their father Roush ibn Abdullah Rahman, 31, and mother Aysha arrived in Riyadh from London by the end of last month.

Prince Abdullah, the regent, had made arrangements to separate the twins and treat them at the Saudi hospital, when their parents failed to raise the cash required for the operation in London.

Before conducting the surgery, a team of psychologists studied the mental condition of both the twins and their parents.

Medical tests proved that separation of the twins — who have independent hearts and lungs — was possible.

The surgery was shown live on the Internet by Prince Sultan Medical Communication and Education Program (MeduNet).