A German humanitarian worker held hostage in the Sahel for more than four-and-a-half years has been freed, his organisation said on Saturday.

Jorg Lange, 63, “can return to his family”, said Bianca Kaltschmitt, director general of the NGO Help, thanking Germany’s foreign ministry, criminal police and the authorities in Mali, Niger and other neighbouring countries for contributing to his release.

Lange was kidnapped by armed men riding motorcycles on April 11, 2018 near Ayorou in western Niger, in a region near the Malian border frequently hit by jihadist attacks.

His Nigerien driver was freed shortly afterwards, but according to German media Lange was sold to the Islamic State in the Greater Sahara group.

German weekly Der Spiegel has reported that the Moroccan secret services’ contacts with jihadist groups in the Sahel facilitated Lange’s liberation, with the humanitarian worker repatriated on an army plane.

At least four Western hostages from France, the United States, Australia and Romania are still detained in the Sahel, according to a tally only covering cases made public by their entourage or governments.

Another German, priest Hans-Joachim Lohre, has been missing since late November and is widely thought to have been kidnapped, although no one has claimed responsibility.

The German government declined to respond to an AFP request for comment. (AFP)