(CNN) -- Conjoined Egyptian twin boys Hassan and Mahmoud, who were successfully separated in Saudi Arabia Saturday, are recovering and are expected to lead normal lives, officials said.

Conjoined twins Hassan, left, and Mahmud rest the day before separation surgery in Riyadh, Saudi Arabia.

"The twins' vital signs are good; they're doing excellent," said Sami Al-Shalan, spokesman for the King Abdulaziz Medical City facility in Riyadh where the surgery took place. "The twins still have about 24 hours before a progress report can be issued. The anesthesia consultants are happy with the progress of the children."

The boys are less than a year old and were brought to the kingdom on February 10. The delicate surgery took a little more than 15 hours.

"The twins' parents have visited them in the [pediatric intensive care unit], but they can't stay there long. They come and go," Al-Shalan said.

Separating the boys' urinary system was a major challenge, Dr. Abdullah Al-Rabeeah, the Saudi minister of health, told CNN. So was separating the siblings' local veins and arteries, he said.

"We had to identify the arteries and the blood veins between each baby," Al-Rabeeah said. Watch Al-Rabeeah explain the operation »

The procedure was the 21st of its kind to be performed in the kingdom.

The surgeries are performed free as part of King Abdullah bin Abdul Aziz's philanthropic initiative.

CNN's Mohammed Jamjoom contributed to this report.

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