Khieu Samphan, former figurehead of the Khmer Rouge, will appeal his pre-trial detention following his arrest Monday, his lawyer said.

"We have decided to file a suit for appeal," lawyer Say Bory said. "Filing this appeal means we do not agree with the [tribunal] ruling."

Khieu Samphan was taken from a Phnom Penh hospital where he was recovering from an apparent stroke in Pailin last week and charged with war crimes and crimes against humanity.

Tribunal judges said Monday they would keep him in detention ahead of his trial.

Researchers say Khieu Samphan's role in the regime was substantial, though he has strongly denied this.