The Islamic State group has said its militants were behind the killing of six French aid workers, their local guide and driver in Niger in August.

A statement from the group has been published by the US-based Site Intelligence Group which monitors extremist violence.

The eight were killed on trip to see some of the last giraffes in West Africa in the Kouré National Park.

Reports at the time said they were shot by gunmen who arrived on motorbikes.

Militant groups, including Boko Haram, operate in the area and violence by groups linked to al-Qaeda and the Islamic State group has been on the rise in the Sahel region.

France has been leading a coalition of West African and European allies against Islamist militants in the region.

The AFP news agency reports that in the message reproduced by Site, the militants said the attack was a "major security lapse" for France.