Doctors said the baby's blood refused to clot, leading to her death.

Earlier surgeons had said baby Rebeca Martinez was doing well after a complex 11-hour operation carried out by a team of 18 people on Friday.

Born with the head of an undeveloped conjoined twin fused to the top of her skull, she was thought to be the first such baby to survive beyond birth.

In the delicate operation, surgeons had to cut off undeveloped tissue, clip the veins and arteries and close Rebeca's skull using a bone graft from another part of her body.

"She was too little to resist the surgery," the baby's mother Maria Gisela Hiciano told the Associated Press news agency from the hospital in Santo Domingo where surgery took place.

The team was led by Jorge Lazareff, who successfully separated Guatemalan conjoined twins in 2002.

A spokesman for the charity Cure International - which is meeting the estimated $100,000 cost of surgery - earlier said that as the surgeons came out of the theatre they had unanimously said the operation was a "great success".

But one of the lead brain surgeons, Benjamin Rivera, told AP the infant had lost a lot of blood in the operation and had many transfusions, but that her blood would not clot.

"In that case, you can't do anything. This is the worst complication that can happen in this kind of surgery," he said.