Norway's King Harald is in a stable condition in hospital after his health deteriorated at the weekend, royal officials have said.

The 89-year-old, who is the oldest living monarch in Europe, was admitted to the National Hospital in Oslo a week ago.

He is receiving antibiotics for a bacterial blood infection and has "responded to this treatment", the royal palace said.

The monarch has been on sick leave for several weeks.

King Harald suffers from a blood disorder and his treatment has led to fluid accumulation in the body that required hospital care, the palace said last week.

He has been in and out of hospital several times in recent years.

Earlier this year, the king was taken to hospital in Tenerife after falling ill on holiday.

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His son, Crown Prince Haakon, has been serving as regent while Harald has been on leave.

King Harald has been monarch since 1991.