France's last remaining hostage, Serge Lazarevic, arrived home Wednesday after three years in the hands of Islamist militants as questions swirled around the terms of his release.

The government has refused to comment on reports that several Al-Qaida prisoners, including those involved in kidnapping Lazarevic in Mali in 2011, were released in exchange for his freedom.

Algeria has begun repatriating thousands of illegal workers to Niger in an operation likely to last several months, the Algerian Red Crescent (CRA) said on Monday.

A first group of 318 arrived at a reception centre on Saturday in the main city in southern Algeria, Tamanrasset, Saida Benhabyles of the CRA told Agence France Presse.

Boko Haram is increasingly a regional threat and the battle against the Nigerian Islamist sect is meant to be a regional campaign -- but that's not the way it feels for Cameroon's soldiers on a desperate frontline.

"We are fed up with fighting this war all alone," a Cameroonian officer said as he described his army's resistance against Boko Haram and the lack of military support from neighbouring governments.

Lawmakers in Niger chose an ex-opposition member to become the new head of parliament on Monday, replacing Hama Amadou who fled to France after being named in a baby trafficking scandal.

Amadou Salifou "was declared elected as speaker of the National Assembly with 71 votes," out of 113, said parliamentary vice-president Daouda Marthe, who has led parliament since Amadou's departure. 

Nigerian Islamist extremists Boko Haram are intensifying attacks in neighboring Cameroon, targeting new villages with increasingly sophisticated weapons, as the army fears more violence in the approaching dry season.

"We're convinced that the establishment of a 'caliphate' (by Boko Haram) is aimed not only at Nigeria but also at Cameroon," Leopold Nlate Ebale, commander for an elite battalion in the border zone, told Agence France Presse.

Twelve children and a villager have been confirmed dead after a hippopotamus attacked a boat near the Niger capital Niamey earlier this week, officials said Wednesday.

The students, aged 12 to 13, died when their boat transporting them across the Niger River was flipped by a hippo on Monday. A number of students in the West African nation take such boats to attend school on the other side of the river.

At least two people died and around 11 schoolchildren were missing Monday after a hippopotamus attacked a boat on the Niger River near the capital Niamey, local authorities said.

"We recovered the bodies of two villagers and counted five survivors, and at least 11 pupils are missing," a local official told Agence France-Presse.

Nine security agents in Niger were killed on Thursday in multiple "terrorist" attacks in the western Tillaberi region near Mali, the government said.

"Terrorists staged simultaneous attacks. Five policemen, two gendarmes and two national guards were killed," the defense and interior ministries said in a joint statement.

Niger said Tuesday its embassy in Libya was surrounded by heavily armed militias, possibly in response to unfounded rumors that Nigerien forces had entered the Libyan embassy in Niamey.

The militias encircled the mission in the capital Tripoli in the early hours of Tuesday, resulting in "diplomatic personnel, including the ambassador, being confined," the secretary general of Niger's foreign ministry, Abani Sani Ibrahim, told reporters.

A U.S. drone crash-landed at Niger's main airport for unknown reasons on Monday, the U.S. army said, forcing the closure of the runway for several hours.

The "hard landing" of the unarmed MQ-9 Reaper aircraft damaged the runway at Diori Hamani International airport in the Niger capital Niamey, but no injuries were reported, according to a statement from the U.S. Air Forces in Europe and Africa public affairs directorate.