Five United Nations peacekeepers from Chad were killed Thursday when their truck drove over a mine in Mali, casting a shadow over peace talks between the west African state and rebel militias.

The attacks follow the restart of negotiations between the Mali government and six armed rebel groups in the Algerian capital aimed at clinching a lasting peace agreement in the deeply-divided nation.

A U.N. peacekeeper from Chad was killed and four others injured when their vehicle struck a landmine in northern Mali on Sunday, officials said.

The killing brought swift condemnation from United Nations Secretary General Ban Ki-moon and in a UN Security Council declaration.

Nigeria and its regional allies on Wednesday called for greater international support to shut down Boko Haram's weapons and funding supply as concern mounted at the group's rapid recent land grab.

The call came after conflicting reports that the militants had seized another town, prompting warnings that Nigeria was losing control of the northeast and violence could spill across borders.

Ten Chadian nationals have been gunned down in southern Libya by attackers in military uniform, the Chadian foreign ministry said Thursday.

"Ten Chadian nationals were shot dead in cold blood in Sbeha by a group of armed men, all of them wearing military uniforms," the ministry said in a statement.

The United States has deployed 80 military personnel to Chad to help regional efforts to rescue more than 200 schoolgirls kidnapped in neighboring Nigeria, President Barack Obama said Wednesday.

"These personnel will support the operation of intelligence, surveillance and reconnaissance aircraft for missions over northern Nigeria and the surrounding area," Obama said in a letter to Congress.

Chad announced it is closing its border with the Central African Republic on Monday, saying it wants to stop violence spilling over from the sectarian conflict next door.

"We will not allow the Chadian territory to be used by one side or the other to wreak havoc in this brotherly country," said government spokesman Hassan Sylla Bakari.

Two civilians were killed when gunmen ambushed a convoy of Muslims fleeing violence in the capital of the strife-torn Central African Republic, international peacekeepers said on Tuesday.

The convoy, bearing some 1,300 Muslims who feared killer raids by mainly Christian vigilantes, left Bangui on Sunday with a strong escort of troops from the African Union's MISCA peacekeeping mission.

Chad said Wednesday it had withdrawn its entire contingent from the Central African Republic, in the wake of accusations its troops had carried out an unprovoked attack in the capital Bangui last month.

"The last soldier crossed the border on April 13," Souleyman Adam, the head of the Chadian unit with the African peacekeeping force MISCA, said at a ceremony in the southern town of Sarh.

Chad on Saturday dismissed as "defamatory and tendentious" U.N. accusations that its troops carried out an unprovoked attack when they opened fire in a crowded market in the Central African Republic's capital, killing at least 30 people.

"The government of the Republic of Chad expresses its surprise and indignation faced with the purported investigation published by the United Nations Human Rights Commission," said a government statement sent to Agence France Presse.

The Central African Republic "regrets" a decision by Chad to withdraw from the peacekeeping force trying to quell sectarian violence in the country, Foreign Minister Toussaint Kongo-Doudou said Friday.

"We learnt with a lot of regret of the announcement... of the withdrawal of Chadian troops from the MISCA (African-led force) in the Central African Republic," he said in a statement sent to Agence France Presse by the CAR embassy in Paris, a day after Chad announced the withdrawal after being accused of siding with a mainly Muslim movement that held power for most of last year.