King Harald V of Norway, 83, will undergo a new heart operation on Friday after weeks of respiratory problems unrelated to Covid-19, the palace said Thursday.

The operation, to be conducted under local anaesthetic, is to fix an artificial valve he received during a previous operation in 2005.

The palace said it was "not rare" to fix such valves, which are only expected to last 10 to 15 years.  Harald, a former Olympic yachtsman who has held the throne for 29 years, has refused to abdicate despite several years of ill-health, including an operation for bladder cancer in 2003.

He was also admitted to hospital for three days late last month due to respiratory problems.  "His Majesty the King has undergone regular checks and our last evaluation shows that this operation is necessary to improve the King's breathing," his doctor Bjorn Bendz said in the palace's statement.

The monarch plays a largely symbolic role in Norwegian society, and Harald's son, 47-year-old prince Haakon, has taken over his functions during the recent period of illness.