The statement did not make clear whether the prince remained in intensive care Friday but said he was "under continuous surveillance." Palace officials said he remains hospitalized.
"His state of health is serious and requires permanent medical care," the statement said.
Tests, X-rays and scans have been carried out to determine the extent of his "acute pancreatic disorder," it added.
News of his condition came as Caroline and Monaco mourn Wednesday's death of the princess' father, Prince Rainier III (search), at age 81 after a monthlong hospitalization. The prince had ruled this Riviera principality, which is smaller than New York's Central Park, since 1949.
His funeral is scheduled for Friday.
Ernst August, Caroline's third husband, is descended from one of Germany's oldest noble families. He is a distant relative of Britain's Queen Elizabeth II (search) and great-grandson of the last German emperor, Wilhelm II.
But he also is renowned as a royal black sheep whose sometimes rowdy, even drunken, behavior has repeatedly landed him in court and in the newspapers.
In 2000, he apologized to the Turkish public for urinating on the side of Turkey's pavilion at the Expo 2000 World's Fair in Germany. Last year, he was convicted and fined for assaulting a hotel owner in Kenya in a drunken rage in June 2000.
German media have dubbed him the "Pugilist Prince." (search)
Doctors did not reveal the nature of the prince's pancreas problem. The two most common are pancreatic cancer and acute pancreatitis, where the pancreas suddenly becomes inflamed.
Pancreatic cancer does not usually come on suddenly, although it can cause acute pancreatitis, said pancreas expert Dr. Stephen Bloom of Imperial College in London.
Most cases of acute pancreatitis are caused by alcohol abuse or gall stones. Like cirrhosis of the liver, pancreatitis is a common affliction of the heavy drinker.
However, in rare cases acute pancreatitis can be caused by injury, prescription drugs, parasites or a virus.
The pancreas is part of the body's hormone production system. It secretes digestive chemicals and insulin, the hormone that carries energy to the tissues.
Ernst August and Caroline, 48, the eldest child of Rainier and Hollywood star Grace Kelly, wed in January 1999 in Monaco's royal palace in a civil ceremony. She is Roman Catholic; he is Protestant. It was the third marriage for her and second for him.
Six months later, Caroline gave birth to a daughter, Alexandra. Between them, Caroline and Ernst already had five children from previous marriages.
Ernst August was not present at a Mass at Monaco's cathedral Tuesday evening in honor of Pope John Paul II, who was buried Friday.
But the prince was seen March 25, standing next to Caroline and her brother, Prince Albert, when they appeared on a palace balcony as a traditional Good Friday procession went past. Although it was dark, Ernst August wore sunglasses.
Caroline's brother, 47-year-old Albert, succeeded his father as the principality's new ruler.