Former U.S. President George H.W. Bush has been moved to an intensive care unit at a hospital in Houston, Texas.

The 88-year-old former president was admitted to the hospital last month suffering from bronchitis. His spokesman says Mr. Bush was moved to the intensive care unit Sunday after a “series of setbacks,” including a persistent fever. The spokesman says Mr. Bush continues to be alert and that doctors are “cautiously optimistic” about his treatment.

The former president's wife, Barbara, and a son and grandson spent Christmas Day with Mr. Bush.

Mr. Bush served as the 41st U.S. president from 1989 to 1993. The highlight of his presidency was the international coalition he assembled that drove Iraqi forces out of Kuwait in 1991.

Mr. Bush also served as a congressman, ambassador to the United Nations, ambassador to China and director of the CIA. He was vice president from 1981 to 1989 under the late President Ronald Reagan.

His sons include the 43rd president, George W. Bush, and former Florida Governor Jeb Bush.