RIYADH, Feb 17 (Reuters) - New York-based Human Rights Watch has called on Saudi Arabia to prevent the execution of an Arab woman convicted of "witchcraft" in the conservative Muslim kingdom. "The religious police who arrested and interrogated Fawza Falih and the judges who tried her ... never gave her the opportunity to prove her innocence against absurd charges that have no basis in law," the group said in a statement sent to Reuters over the weekend.

An appeals court ruled in September 2006 that the illiterate woman could not be executed because she had retracted a confession allegedly made after weeks of beatings.

But a lower court subsequently said she should be executed in the "public interest", the rights group said.

Falih, 51, is a Saudi citizen of Jordanian origin who lived in the remote desert town of Qurayyat near Jordan.

Saudi Arabia imposes a hardline version of Islamic law but has no written penal code and judges have wide discretionary powers in sentencing.

Executions are carried out by public beheading for murder, rape, drug trafficking and armed robbery, and sometimes charges such as sorcery and witchcraft.

Clerics, who also serve as judges, take witchcraft seriously and last year an Egyptian man was executed for using such means to try to split up a couple.

King Abdullah has promised wide-ranging judicial reforms but observers say they could take years to implement. (Reporting by Andrew Hammond; Editing by Catherine Evans)