French anti-terrorist prosecutors announced Monday an investigation of an attack on a sightseeing excursion in Niger, West Africa that left six French citizens dead.

The deadly rampage Sunday was carried out by men on motorcycles armed with rifles who appeared by surprise out of the bush. Most of the French victims were employees of ACTED, a French humanitarian group.

Two Nigerians were also killed in the attack: the guide, who led the local Association of Giraffe Guides, and the driver of the excursion vehicle.

The attack took place when the group was out to view local giraffes around the town of Koure, 60 kilometers (37 miles) east of Niemey, the country’s capital.

The West African country has seen growing terrorism over the past three years, with Boko Haram and al-Queda in the Islamic Maghreb (AQIM) carrying out attacks in neighboring Mali, where other terrorist groups have also operated. A total of 20 civilians were also killed in the region this May.

France has had military forces installed in the Sahel since 2014 in Operation Barkhane. Approximately 5,000 troops are stationed in N’Djamina, the capital of neighboring Chad, operating with the cooperation of what is known as the G5 Sahel, the five West African countries and former French colonies of Niger, Chad, Burkina Faso, Mauritania, and Mali.

The effort at stabilization and neutralizing any terrorist activity remains strong as the G5 Sahel lie directly south of France and Europe.

President Emmanuel Macron spoke about the deadly attack by phone Sunday evening with his Nigerien counterpart Mahamadou Issoufou.

A statement on Monday from the Elysee Palace conveyed the urgency to uncover the motivation for the murders.

“Their determination to continue the common fight against terrorist groups in the Sahel remains intact,” said the statement.

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