The European Union on Thursday demanded the "immediate release" of Niger's President Mohamed Bazoum and his family after elite troops detained him and declared they had taken power.

"Niger is an essential partner of the European Union in the Sahel, whose destabilisation would not serve the interest of anyone in the country, the region or beyond," spokeswoman Nabila Massrali said.

EU chief Charles Michel posted online that he had vowed the bloc's "full support" for Bazoum in phone calls with Niger's leader on Wednesday.