FILE PHOTO: Saudi Arabia's Crown Prince Mohammed bin Salman leaves the Hotel Matignon in Paris, France, April 9, 2018. REUTERS/Charles Platiau/File Photo

GENEVA (Reuters) - The United Nations called on Saudi Arabia on Tuesday to provide information about women’s rights activists arrested ahead of the lifting of a ban on women driving that is part of Crown Prince Mohammed bin Salman’s reform program.

The U.N. human rights office said the government should ensure the women and other campaigners in custody have due process.

The crackdown on women’s rights activists, just weeks before a much-hyped lifting of the has revived doubts about Prince Mohammed approach to reforms in the kingdom.

Nearly a dozen prominent activists, mostly women who for years urged reforms that are now being implemented, were arrested this month, drawing a rare expression of concern from the U.N. human rights office on Tuesday.

Six women and three men are known to remain in custody facing very serious allegations that “could lead to draconian sentences”, U.N. human rights spokeswoman Liz Throssell told a Geneva briefing.

Their exact whereabouts is unknown and most of them have only been permitted to make a single telephone call to their families since they were arrested, she said.

“We urge the Saudi Arabian authorities to reveal their locations, and ensure their rights to due process guarantees,” Throssell said. “If, as it appears, their detention is related solely to their work as human rights defenders and activists on women’s issues, they should be released immediately.”

They are entitled to the right to legal representation, to know the nature of the charges against them, to have access to their families and to be brought before an impartial tribunal within a reasonable period of time, she added.

Saudi authorities should provide information about a Saudi prince, Nawaf Talal Rasheed, reported to be missing since being deported from Kuwait on May 12 and to make clear if was arrested and on what grounds, she said. He is also Qatari national.