PARIS (AP) — French anti-terrorism prosecutors formally opened an investigation one day after eight people, including six French nationals, were killed by gunmen in a Niger giraffe park.

Seven of the eight people were aid workers working in the West African country, two European aid groups said Monday.

The six French citizens and one Nigerien were working for Paris-based NGO ACTED and Geneva-based IMPACT Initiatives. The other victim was their Nigerien guide.

The NGOs condemned “in the strongest terms the senseless and barbaric killing of our colleagues and their guide.”

French prosecutors said in a statement Monday they opened an investigation for “murders in relation to a terrorist undertaking.”

Niger’s interior ministry said Sunday the attack took place in Koure, where the aid workers were visiting a giraffe reserve. Hundreds of people visit each year the protected national park that contains dense vegetation and tall trees about 70 kilometres (45 miles) southeast of the capital.

“Our colleagues have been working to support the people of Niger facing hardship, driven by values of humanity and solidarity,” the NGOs said.

This August 9, 2020 image shows the wreckage of the car where six French aid workers, their local guide and the driver were killed by unidentified gunmen riding motorcycles in an area of southwestern Niger. Gunmen on motorcycles killed eight people including a group of French aid workers as they visited a part of Niger popular with tourists for its wildlife. (Photo by BOUREIMA HAMA/AFP via Getty Images)

This August 9, 2020 image shows the wreckage of the car where six French aid workers, their local guide and the driver were killed by unidentified gunmen riding motorcycles in an area of southwestern Niger. – Gunmen on motorcycles killed eight people including a group of French aid workers as they visited a part of Niger popular with tourists for its wildlife. (Photo by BOUREIMA HAMA / AFP) (Photo by BOUREIMA HAMA/AFP via Getty Images)

The Association of Giraffe Guides of Koure also released a statement condemning the death of the president of their association, Kadri Abdou.

“We are deeply saddened and thinking of the victims and their families to whom we offer our most sincere condolences and especially to the family of Kadri, our friend. May he rest in peace,” said the statement.

One of the biggest French NGOs, ACTED has been present in Niger since 2010 and provides aid to displaced people and local populations who are particularly vulnerable due to conflicts in the region, lack of food and droughts.

A partner to ACTED, IMPACT Initiatives was first deployed in Niger in 2012. It conducts mapping programs and other projects in camps hosting displaced populations.

In a phone call on Sunday, French President Emmanuel Macron and Niger President Mahamadou Issoufou pledged to clarify the circumstances of the deadly attack by “all means,” the French presidency said.

French Foreign Affairs minister Jean-Yves Le Drian condemned the attack on Monday, saying that those responsible “will have to answer for their acts.”

The ministry’s crisis centre and the French embassy in Niger are fully mobilized to support the victims’ families, he said.

The French government has warned citizens against travelling outside Niger’s capital, Niamey, as militants linked to Boko Haram, Islamic State and al-Qaida carry out attacks across the vast West African nation. Niger borders several countries including Mali, Burkina Faso, Chad, Nigeria and Libya.

Violence by rebels linked to the IS group and al-Qaeda is on the rise in the Sahel region. France has deployed 5,100 soldiers to help fight the growing insurgency there, and a local Sahel force made up of soldiers from Mali, Niger, Burkina Faso, Chad, and Mauritania has also been fighting the extremists.

Members of the NGO Acted (from L) Frederic de Saint Cernin, co-founders Frederic Roussel and Marie-Pierre Caley, and their lawyer Joseph Breham arrive to give a press conference in Paris, on August 10, 2020 following the death of eight people including French aid workers, killed by a gunman while visiting a part of Niger on August 9, 2020 that is popular with tourists for its wildlife. (Photo by MARTIN BUREAU/AFP via Getty Images)

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Petesch reported from Dakar, Senegal.

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