German aid worker Jorg Lange was freed on Saturday more than four and a half years after Islamic extremists kidnapped him in the West African country of Niger, according to Help, the German aid organisation where he works.

The group’s statement did not provide details of how or where Lange, a 63-year-old engineer, was released.

“We are very relieved and grateful that our colleague Jorg Lange can return to his family after more than four and a half years,” said Bianca Kaltschmitt, the organisation’s managing director.

Lange, the Niger country director for Help, was kidnapped by the Islamic State group in Niger’s Tillaberi region in April 2018. Help said Lange has dedicated more than three decades of his life to humanitarian assistance.

For seven years jihadi groups linked to al-Qaida and the Islamic State group in the Sahel, the vast expanse south of the Sahara Desert, have been been using hostages held for ransom as a way to fund operations and expand their presence.

“The Sahel region has proven to be an unstable region for missionaries and foreign workers alike with the backdrop of several hostage-taking incidents and the proliferation of militancy over the past few years,” Laith Alkhouri, CEO of Intelonyx Intelligence Advisory which provides intelligence analysis, said on Saturday.

 “Taking hostages has proven to be a lucrative business that bankrolls terrorist groups, but also amps their notoriety,” he said.

At least 25 foreigners and untold numbers of locals have been abducted in the Sahel since 2015, according to the Armed Conflict Location & Event Data Project. Five foreigners remain captive according to the organisation, including Reverend Hans-Joachim Lohre, a German priest kidnapped in Mali’s capital Bamako in November.

Others still detained include French journalist Olivier Dubois, who was kidnapped last April from northern Mali, US national Jeffery Woodke, Australian doctor Ken Elliott and Romanian national Iulian Ghergut, who was abducted from a mine in Burkina Faso and has been held since 2015. - AP