RIYADH (AFP) - A 15-year-old Saudi girl who was forced to marry an octogenarian has been granted a divorce after a local human rights group intervened, the watchdog said on Wednesday.

The Saudi Human Rights Commission (SHRC) raised the case "after learning of the marriage of a minor girl to an 86-year-old man in Jizan" in south-east Saudi Arabia, the group's head Bandar al-Ayban said in a statement.

Al-Hayat daily had reported that the teenager locked herself inside the bedroom on her wedding night before fleeing the man's home and returning to her parents.

She had been married off to the man in exchange for a dowry worth around US$17,300 (S$21,225), the daily reported.

The SHRC had provided "legal assistance to the girl" so she could get a divorce, Ayban said.

Another SHRC member, Hadi al-Yami, said the girl had "expressed her rejection of this marriage." The divorce was announced after a regional tribal chief and local dignitaries intervened.

Saudi rights officials have been pushing for a law that would set a minimum marriage age of 16.

The SHRC is "trying in cooperation with ministries of justice and health to prevent such marriages," Yami told AFP.

Rights activist Suhaila al-Hammad says the authorities must "set the minimum marriage age at 18." Saudi Arabia has no law against child marriage, and clerics and religious judges justify the practice based on Islamic and Saudi tradition.