Former Chadian dictator Hissene Habre refused to answer questions at a hearing Wednesday ahead of his trial for a string of atrocities he is accused of committing during his presidency, his lawyer said.

Once dubbed "Africa's Pinochet", the 72-year-old has been in custody in Senegal since his arrest in June 2013 at the home he shared with his wife and children.

A soldier in fatigues furiously pedals his bicycle through the alleyways of Diffa, puffing away after the biggest town in southeast Niger banned motorcycles -- vehicle of choice of jihadists.

Situated on the border with northeastern Nigeria, the heartland of Boko Haram insurgents, Diffa is on high alert since it was attacked in February.

Nigeria's new President Muhammadu Buhari will this week make his first foreign trip since taking office, traveling to Chad and Niger for talks on Boko Haram, his spokesman said on Monday. 

Shehu Garba said the two-day trip starting on Wednesday will focus on "matters of security", with the cooperation of Nigeria's neighbors seen as crucial to ending the Islamist uprising which has claimed more than 15,000 lives since 2009. 

Nigeria's military on Saturday repelled a Boko Haram attack on the key northeastern city of Maiduguri, a day after President Muhammadu Buhari took office vowing to crush the group, witnesses and security sources said.

The overnight attack on the Borno state capital saw rocket-propelled grenades fired into homes in a bombardment that reportedly lasted several hours.

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.

Chad's President Idriss Deby has called for better coordination between coalition forces fighting Boko Haram in northeast Nigeria, warning that the group has been wounded but not defeated.

"If we still have to fight and catch (Boko Haram leader) Abubakar Shekau, the armies have to work together," Deby said on a visit to Nigeria's capital Abuja on Monday to meet outgoing President Goodluck Jonathan.

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.

Suspected Boko Haram insurgents have forced hundreds of soldiers to flee Marte, a border town along the shores of the Lake Chad, a local official and witnesses said Friday. 

"The terrorists, numbering over 2,000, appeared from various directions on Thursday and engaged the soldiers in Kirenowa town and adjoining communities in Marte," said Imamu Habeeb, a local community leader.

Nineteen people were killed in Thursday night's attack on a Cameroonian village by Nigeria-based Boko Haram militants, a security source said in an updated toll, adding that most of the victims were beheaded.

"The final toll from this attack is 19 dead, with a majority of the victims decapitated," a security source said Saturday on condition of anonymity.