A clash between Chad's army and Boko Haram on a Lake Chad island has killed four soldiers and 33 Islamists, a military spokesman said Friday.

"Boko Haram elements on Wednesday attacked our forces in Choua," military spokesman Colonel Azem Bermandoa Agouna told AFP, referring to a Lake Chad island in Chadian territory.

A fundraising campaign to help Cameroon's army battle Nigeria's feared Boko Haram fighters has brought in more than three million euros and hundreds of tonnes of food, local media said Wednesday.

"2.1 billion CFA francs (3.2 million euros) already" collected to help troops fighting the Islamist group on Cameroon's northern border with Nigeria, said the national CRTV radio and TV network.

Niger has extended for three months the state of emergency in its southeastern Diffa region where the army has been battling Boko Haram militants since February, authorities announced Wednesday.

"Boko Haram elements are there," Daouda Malam Marthe, first vice president of parliament, said on state radio. "The prolongation of the state of emergency is a necessity."

A journalist and rights activist known for his outspoken criticism of the humanitarian crisis in southeastern Niger has been arrested for "collaborating" with Boko Haram Islamists, the interior minister said Wednesday.

Human rights watchdog Amnesty International condemned Moussa Tchangari's arrest and called on Niger to release him.

Several shelters are to open in Niger for illegal African immigrants in a bid to dissuade them from trying to reach Europe and instead offering local alternatives, the French interior minister said Friday.

The centers proposed by the European Union, in cooperation with Niger, "should be an opportunity to bring ambitious development policies for migrants and for states," said Bernard Cazeneuve in Niger's capital Niamey after meeting President Mahamadou Issoufou.

Two soldiers from Cameroon have been killed and at least two others wounded in an attack by Boko Haram fighters near the Nigerian border, security sources told AFP on Monday.

Speaking on condition of anonymity, one Cameroonian military officer said two troops were killed, and an officer and a soldier injured in a clash on Saturday with the Islamists.

Burkina Faso and Niger have announced they will exchange 18 towns in order to settle a long-running border dispute and end years of litigation.  

Burkina Faso is to gain 14 towns and Niger will receive four between now and the end of 2016 when the drawing of the boundary is complete, Kouara Apiou Kabore, the permanent secretary of the Burkina Faso National Border Commission said this week.     

Around 25,000 Niger nationals who fled islands in Lake Chad over fears of attack from the Boko Haram jihadist group are living in "dramatic" conditions on the mainland, a U.N. source said Wednesday.

Citing security fears, Niger authorities last week urged residents of islands on the Niger side of the vast lake to evacuate by Monday.

Niger authorities have urged people living on islands in Lake Chad to leave to avoid new attacks by Boko Haram, after an assault by the Islamists last weekend left at least 74 dead.

The weekend attack was the country's heaviest loss since it joined a regional offensive against the militants, and saw authorities declare three days of mourning from Wednesday.

Long tailbacks form at a bridge on the border between Chad and Cameroon while Chadian security forces, wary of deadly Boko Haram jihadists, screen all road users and their property.

"We're looking for weapons," a police officer explains at the Ngueuli bridge on the main road for imports to landlocked Chad, linking the capital N'Djamena to the far north of Cameroon.