Seven gendarmes have been killed in an attack on a refugee camp in Niger hosting civilians who have fled Boko Haram, security and humanitarian sources said Friday.

Thursday's attack at the southeastern Nguagam camp, home to both internally displaced Nigeriens and refugees from across the border in Nigeria, came shortly after a major visit by lawmakers and UN personnel.

"Seven gendarmes were killed. They were buried today," a humanitarian source, speaking on condition of anonymity, told AFP. A security source confirmed the toll.

"Three Boko Haram vehicles arrived in the area," El Hadj Kilibou, one of the camp's residents, told AFP.

"They went to attack the position of the gendarmes, who abandoned their post. They took the vehicles and set fire to the gendarmes' camp," added Kilibou.

"They were wearing gendarmes' uniforms and were onboard gendarme vehicles. I saw it with my own eyes. They said to me, 'Don't run, stay, we're not killing civilians.'"

Kilibou fled a massive Boko Haram attack in the town of Bosso on June 3 that left 26 Nigerien and Nigerian soldiers dead as well as numerous civilians, prompting 50,000 people to flee.

Humanitarian and security sources said the Islamist group had infiltrated the camp, just a few kilometres from the Nigerian border, in order to watch what is happening there.

Boko Haram's seven-year insurgency has left at least 20,000 people dead in Nigeria and made more than 2.6 million homeless in its quest to form a hardline Islamic state.

Extending the attacks to neighbouring countries from their base in northern Nigeria, the group's ascendancy has prompted a regional military fightback from Niger, Chad and Cameroon.