NIAMEY, NIGER -- Unidentified gunmen killed six French aid workers and two Nigerien guides who were visiting a wildlife park east of Niger's capital early Sunday, authorities from both countries said.

French President Emmanuel Macron expressed his condolences and support for the victims' families in a statement.

Macron had a phone call with Niger President Mahamadou Issoufou on Sunday evening and both heads of state stressed that "all means are and will be used to clarify the circumstances of the deadly attack," the statement said.

Macron and Issoufou are determined to "continue the fight against terrorist groups" in Africa's Sahel region.

The attack took place in Koure, where Niger has a giraffe reserve, Oumarou Moussa, the adviser to Niger's interior minister, told The Associated Press. The area is a protected national park that contains dense vegetation and tall trees about 70 kilometres (45 miles) southeast of the capital. Hundreds of people visit each year to see its distinctive giraffes.

The park is in the Tillaberi region, where jihadists linked to Islamic State killed four U.S. soldiers and five Nigeriens in 2017.

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

Violence by groups linked to IS and al-Qaida 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.

Macron will hold a defence council on Tuesday focusing on the situation in Niger.