DALLAS (Reuters) -- One week after doctors separated 2-year-old Egyptian twins conjoined at crown of the head, one of the boys has been taken off a mechanical ventilator and their condition may soon be upgraded from critical to guarded, doctors said on Sunday.

Dr. James Thomas, director of critical care at Children's Medical Center in Dallas where Ahmed and Mohamed Ibrahim were separated last Sunday, said Mohamed was taken off a ventilator that had helped him to breathe and his brother may be removed from the apparatus on Monday. "If Ahmed continues to improve, he may be ready to come off the ventilator tomorrow," Thomas said. "Once each twin is breathing on his own without respiratory distress, his condition may be upgraded from critical to guarded."

Ahmed suffered some seizures on Friday night and has not recovered as quickly as his brother from a 34-hour operation in which a team of five neurosurgeons separated some brain material the boys shared as well as the shared circulatory systems that feed blood to their brains.

Thomas said Ahmed has had no further seizures since Friday night and both boys were running a low-grade fever.

There were no signs of infection, one of several medical conditions that could threaten their lives in the crucial post-operative period.

Both boys are still weak but are showing more movement in their limbs. They both are responsive to verbal stimulus, he said.

The boys lie under sedation in separate rooms on beds designed to rotate their bodies so that they do not develop bed sores.

"The neurosurgical and medical teams are very pleased with the twins' progress so far. However, these boys are still at a critical stage in their recoveries and therefore are kept in an environment that minimizes stimulation," Thomas said.

The boys were born in a town 500 miles south of Cairo on June 2, 2001.

Twins conjoined at the head account for about one of every 2.5 million births and about 2 percent of all conjoined births.