The king is suffering from “a low heart rate”, which will require a permanent pacemaker to be implanted once he is free from infection, a palace statement said.

“This could take several days, so the king is likely to remain at Rikshospitalet until after the weekend,” it said.

The infection “has recently become more under control”, and “his condition is stable and improving”, it added.

Europe’s oldest reigning monarch, King Harald fell ill with an infection while on a holiday on the Malaysian island of Langkawi.

He was hospitalised for several days before a medical transport flight flew him home to Oslo on Sunday.

On Saturday, the king was fitted with a temporary pacemaker, which his personal physician said would make his return safer.

Harald needs crutches to get around and has suffered a series of health issues in recent years.

He caught a respiratory infection in January, days after dismissing speculation that he might abdicate, following the lead of his 83-year-old distant cousin Queen Margrethe II in Denmark.

King Harald has been monarch for 33 years, and celebrated his 87th birthday on February 21st.

The royal palace said on Sunday that the king had been placed on sick leave for two weeks. Crown Prince Haakon, 50, has stepped in as regent in his
absence.