PARIS (Reuters) - A French judge will investigate the disappearance in Syria of a father and son of dual French and Syrian citizenship, a judicial source said, in the first French probe into crimes for which rights groups blame the government of President Bashar al-Assad.

The investigation into alleged torture, forced disappearance and crime against humanity was opened following a complaint filed on Monday by two rights groups and Obeida Dabbagh, brother and uncle to the missing pair, Patrick and Mazzen Dabbagh.

"It is time that judicial authorities in other countries investigated the crimes committed by the regime of President Bashar al-Assad," the FIDH and LDH rights groups said in a statement.

They said the father and son were arrested in November 2013 by soldiers.

(Reporting by Gerard Bon; Writing by Ingrid Melander; Editing by Andrew Roche)