Sudanese twins born with their heads joined have been separated in a series of risky operations at a London children's hospital, a global charity said Sunday.

Craniopagus twins Rital and Ritag Gaboura, 11 months old, make one out of very rare cases of twins joined at their heads. Twins like them are born in 2.5 million births.

A charity helping disfigured children, Facing the World, made arrangements for and helped fund the four-stage surgery of the twins.

The twins' operating team noted there's significant blood flow between their brains, making the surgery very risky.

"Incidences of surviving twins with this condition is extremely rare," lead surgeon David Dunaway said in a statement released by the charity. "The task presented innumerable challenges and we were all very aware of our responsibilities to the family and these two little girls."

Facing the World released to New York Times 'before' and 'after' photographs of the girls. The before photo showed the two lying across a bed, with their heads joined just above their hairline.

Facing the World said that separation took place in stages at London's Great Ormond Street Hospital, with two operations in May, the insertion of tissue expanders in July and the final separation on Aug. 15.

"Within days the twins were back on the general ward interacting and playing as before," the charity said. Its executive coordinator, Sarah Driver-Jowitt, predicted that the girls' parents (whom the charity did not name) may soon return home "with two healthy, separate girls."

There have been successful separations for craniopagus twins in the past. In 2004, Filipino twins joined at their heads had a successful surgery at New York's Montefiore Children's Hospital. In 2003, surgeons in Dallas successfully separated 2-year-old Egyptian craniopagus twins.

The New York Times reported one of the first successful operations to separate craniopagus twins happened in 1956, citing records at the U.S. National Library of Medicine.