The health of King Harald of Norway deteriorated over the weekend, the royal palace said.
The 89-year-old, who has been on sick leave for several weeks, was admitted to the National Hospital in Oslo a week ago where he was receiving antibiotics for a bacterial blood infection and had responded to treatment, the palace said late on Sunday
The palace added that his condition was stable.
His son, Crown Prince Haakon, has been serving as regent during this time, the palace said.
The king suffers from hemolytic anemia and was being treated with cortisone, leading to fluid accumulation in the body that required hospital treatment, the palace said last week.
Norway’s prime minister sent his wishes for the king and said that “all of Norway is following and thinking about the king”, public broadcaster NRK reported.
“My strong wish is that he continues to receive good treatment from the good healthcare system we have,” Prime Minister Jonas Gahr Store said.
Harald, who has been monarch since 1991, has been in and out of the hospital several times in recent years.
In February, he was admitted to a hospital in Spain’s Canary Islands during a winter holiday for treatment for a skin infection.
Two years ago, the king fell ill during a private holiday with the queen in Malaysia and received a temporary pacemaker there.
Harald returned aboard a medical airplane to Norway, where he was fitted with a permanent pacemaker.