Rifle-toting Cambodian police arrested ex-Khmer Rouge President Khieu Samphan on Monday, the latest member of Pol Pot's inner circle to be detained by the U.N.-backed Killing Fields tribunal.

The French-educated guerrilla leader was taken from a hospital in the capital Phnom Penh where he was treated after suffering a fall last week at his home in the former Khmer Rouge stronghold of Pailin on the Thai border.

My client is being transferred to the tribunal today where he will appear before the co-investigating judges, Say Bory, Khieu Samphan's lawyer, told Reuters.

A court spokesman declined to comment, but a Cambodian judge on the tribunal also confirmed the transfer.

A close confidante of Pol Pot, the 78-year-old Khieu Samphan has denied knowledge of any atrocities committed by the Khmer Rouge during its four-year reign of terror from 1975-79.

An estimated 1.7 million people were executed or died of torture, disease or starvation under the ultra-Maoist revolution. His 24-year-old daughter said she was not allowed to see her father before his arrest.

I don't know why they won't let my father go back home, Khieu Maly told Reuters.

Khieu Samphan is the fifth person to face the long-awaited Khmer Rouge tribunal, which started work in earnest a few months ago after nearly a decade of delays caused by wrangling over jurisdiction and cash.

Former Foreign Minister Ieng Sary and his wife -- both life-long friends of Brother Number One Pol Pot -- were arrested and charged last week with crimes against humanity.

Brother Number Two Nuon Chea, who had also lived in Pailin, is in the custody of the court on similar charges, as is the Beijing-backed regime's chief jailer, Duch, who ran Phnom Penh's S-21 torture and interrogation centre.

Duch will be the first to make a public appearance at the tribunal when he appears for a bail hearing on Tuesday.

Khieu Samphan was the leading intellectual among the small group of Cambodian students in 1950s Paris who became imbued with communism and returned home to the southeast Asian nation to form the core of the guerrilla movement that became the Khmer Rouge.

However, he published a book three years ago portraying himself as a virtual prisoner of the regime and denying knowledge of any atrocities as Pol Pot drove his dream of creating an agrarian peasant utopia.

Pol Pot died in 1998 in the final Khmer Rouge redoubt of Anlong Veng.

(Writing by Darren Schuettler; editing by Rosalind Russell)