- How did the attack unfold? -

Attackers on motorbikes shot their victims -- six humanitarian aid workers from the French NGO Acted, their driver and a local guide. One of the dead had her throat cut.

The group were attacked at a nature reserve about 60 kilometres (40 miles) from the capital Niamey.

Although a co-founder of Acted suggested it was an opportunistic attack, French General Dominique Trinquand said it was likely to have been a targeted raid backed by some intelligence.

"It's typical of jihadists to arrive on motorbikes armed with Kalashnikovs, launching an attack before leaving immediately in different directions," he told AFP.

The jihadists had favoured hostage-taking until recently, but such operations have become riskier because of the huge regional anti-jihad deployments -- more than 5,000 French personnel along with a joint force set up by five West African countries known as G5.

"They know very well that they have little chance of getting away. So they kill," Trinquand said of the jihadists.

- Who were the attackers? -

The assailants vanished without a trace despite a manhunt backed by French Mirage aircraft and a drone.

No group has said it carried out the attack. Suspicion has fallen on the Islamic State in the Great Sahara (ISGS), which has suffered recent losses at the hands of the French military.

"The barbarity and the conduct of the massacre do indeed bear the hallmarks of the ISGS," says Niagale Bagayoko of the African Security Sector Network, a think-tank and advisory group.

French interests in West Africa could also be the target of Al-Qaeda in the Islamic Maghreb after French soldiers killed its leader Abdelmalek Droukdel in June. But AQIM has denied involvement in the attack in Niger, according to media reports.

- What are the wider effects? -

French President Emmanuel Macron vowed Tuesday to reinforce security measures in the region and the next day France advised against any travel to areas of Niger outside Niamey.

The French army and its allies in the G5 have killed dozens of jihadists in recent months, leading some to claim that the tide had turned against militant groups in the region.

But local and French forces still suffer regular attacks.

Accusations of abuses by local forces coupled with turmoil in Niger's vast neighbour Mali -- where the president is facing mass protests and demands to step down -- complicate the fight against the jihadists.