A Scandinavian Airlines medical evacuation plane has arrived in Malaysia’s northern resort island of Langkawi, where the Norwegian king is being treated for an infection.

King Harald V, Europe’s oldest monarch at 87, was taken to hospital after he fell ill during a holiday, the royal palace in Oslo announced on Tuesday.

There were no details of his illness. His son, Crown Prince Haakon, has said his father’s condition was improving and that he needed rest before being brought back.

Norwegian TV2 said that a Scandinavian aircraft with the tail number LN-RPJ took off from Oslo Airport on Thursday. The Boening 737-700 airliner, which has previously been used as a flying ambulance, landed in Langkawi on Friday.

The Norwegian Defence Force reportedly declined to confirm if the plane will pick up King Harald.

Norwegian TV2 said the same aircraft was used last summer for the medical evacuation of patients from Ukraine.

Malaysian national news agency Bernama has reported that Harald was undergoing treatment at the Sultanah Maliha Hospital in Langkawi. It cited unnamed sources as saying he was staying in the hospital’s Royal Suite. The hospital declined to comment when contacted by The Associated Press.

Prince Haakon said on Wednesday that the king was in good spirits.

“It is clear that his age means that it is good to treat this properly. They are very good at the hospital,” Haakon told Norwegian reporters.

“We don’t know when he will come home. We will have to decide on that later.”

Two days before his birthday last week, Norwegian news agency NTB said that the king would be undertaking a private trip abroad together with his wife Queen Sonja, without specifying the destination or dates.

The monarch, who has been seen using crutches in recent years, has been repeatedly ill in recent months, raising concern about the head of state’s health. In January, the palace said he was on sick leave until February 2 because of a respiratory infection.

In December, he was admitted to a hospital with an infection and was treated with intravenous antibiotics. He also was taken to hospital last August with a fever.

Earlier, Norwegian Prime Minister Jonas Gahr Store said that “we get worried when our king gets ill and is admitted to hospital, whether in Norway or abroad”.

“We should do what we can to contribute to getting the king home as quickly as possible and as healthy as possible,” he told Norwegian broadcaster NRK.