A critical phase in the operation of conjoined Iranian twins has been successfully completed, doctors in Singapore say.
There were some unexpected delays during the first phase of the surgery
Neurosurgeons have re-routed a shared vein that drains blood from the twin sisters' brains - and which had been considered the major obstacle in the unprecedented operation.
"We will be making the announcement later today, provided there are no changes in circumstances," a spokeswoman for Singapore's Raffles Hospital told BBC News Online.
Other than sharing the finger-thick vein, the women's brains are not joined, although they touch inside their skulls.
The bodies of Laleh and Ladan Bijani are otherwise distinct.
Before dawn, surgeons began stitching a vein taken from Ladan's thigh to one of the twin's brains to compensate for the removal of the shared vein, chief surgeon Doctor Kumar said.
Classical music played softly as surgeons worked simultaneously in tight spaces in front of and behind the twins, who are sitting in a custom-built brace connected to an array of lines feeding them intravenously and monitoring their vital signs, he added.
Thoughts and prayers
Iranians living in Singapore and around the world have gathered at Singapore's Raffles Hospital to pray for the Bijani sisters as they undergo world-first surgery to be separated after 29 years joined at the head.
"I hope it will be successful and we pray a lot and we read the Koran," Azimi Shahin, 50, a businessman who has lived in Singapore for 20 years, said after taking time off work to come to the hospital on Monday.
Mr Shahin said the hospital had set aside a room on the second floor of the hospital where about 15 Iranian expatriates gathered on Sunday to pray at the start of the marathon operation.
Another Iranian living in Singapore, university lecturer Habib Hosseini, said he had come to the hospital on Monday to offer his blood in case the twins needed it.
"I have not met them ... I came to support just because I am Iranian," Mr Hosseini said.
Iran's diplomatic community in the region was also offering its support, with the Iranian ambassador to Jakarta, Shaban Shahidi Moadab, expected to arrive at the hospital on Monday evening, an embassy official said.
A team of 28 doctors and 100 medical assistants are involved in the surgery.
After the separation the doctors will do the final surgical reconstruction of the skin and soft tissue on the exposed area of their heads, using muscle and skin grafts.
The twins have been told they have a 50-50 chance of survival but say they are willing to risk death for the chance to lead separate lives.
The Bijanis long to see each other's faces
The operation marks the first time surgeons have tried to separate adult craniopagus twins - siblings born joined at the head - since the operation was first successfully performed in 1952.
German doctors had turned away the Bijanis in 1996, deeming the operation too risky.
The chief surgeon at Raffles, Dr Keith Goh, said he had weighed up quality of life against risk before he could proceed.
The petite Iranian sisters said they knew about the risks, but were still keen to go ahead with an operation they have wanted for years.
Now aged 29, they have become well-known in their home country for their courage and academic success - both are law graduates.