The move was the latest twist in a complicated power struggle involving Sultan Tengku Ismail Petra and his family, one of Malaysia's most prominent royal households.

The sultan, who has battled heart problems for nearly a year, was hospitalized in his northern home state of Kelantan on Tuesday after state authorities refused to let one of his sons, Tengku Muhammad Fakhry, take him to Singapore for medical treatment.

Sultans and rajas are the hereditary titular heads in nine of Malaysia's 13 states. They are widely respected among the ethnic Malay Muslim majority, but their responsibilities are largely ceremonial and the power to govern rests with Parliament and elected state legislatures.

A team of top Malaysian lawyers filed an application Friday in a special court reserved for royalty seeking the sultan's release from the hospital. They said they had received instructions from the sultan, but declined to say how.

“We take the view that the sultan is in hospital under restraint,” said lawyer Raja Aziz Addruse.

In a statement filed to the court Friday, Fakhry alleged the sultan wanted to travel to Singapore earlier this week, but dozens of armed security personnel forced his vehicle to stop while he was heading from the palace to the airport and whisked him away to the state hospital.

There was no immediate date scheduled for a court hearing.

Kelantan's hospital and police officials declined to comment on the lawyers' statements.

Fakhry has been embroiled in a feud with his eldest brother, Tengku Muhammad Faris, the state's crown prince.

Faris has been Kelantan's titular head after their father fell ill, and he removed Fakhry last September from the state's powerful Council of Succession, which determines who ascends to the throne.

Faris ordered police to step up security for the sultan at the hospital Wednesday, but palace officials loyal to him have insisted they were acting in the sultan's best interests.