People stand behind burned cars following an attack at a car park in Maiduguri, Nigeria, Friday. (Hamza Suleiman/AP)

Battling multiple bombers who had strapped themselves with suicide vests Friday, Nigerian troops and civilian self-defense fighters repelled the fiercest Boko Haram attack in months on the key northeastern city of Maiduguri.

Nine bombers and two civilians were killed, according to witnesses, soldiers and police.

The United Nations said the extremist attackers targeted refugees in the city that is the birthplace of the Islamist uprising and the headquarters of the military campaign to halt it.

Friday’s targets were a site hosting more than 9,000 refugees and a garage where some have gathered to try to find transportation home, Farhan Haq, deputy spokesman for the United Nations secretary general, told reporters in New York.

“These are not the first attacks affecting the most vulnerable people,” Haq said.

Residents in Maiduguri awoke to mighty explosions around midnight. Three female suicide bombers blew themselves up at a truck station, detonating vehicles at Muna Garage on the city’s eastern outskirts, according to police Deputy Superintendent Victor Iskukwu.

Two civilians died in the blasts and seven self-defense fighters were wounded, witness Ayuba Ibrahim told the Associated Press.

“Most of the trucks that were loaded with goods for export to Chad and the border communities were destroyed, along with commodities worth millions of naira,” Ibrahim said, referring to the Ni­ger­ian unit of currency.

One blast occurred as people were trying to board the trucks, said resident Isa Mamman.

The attack also targeted a military checkpoint, according to Ahmed Satomi of the Borno State Emergency Management Agency.

Soldiers later fired at gunmen on motorcycles escorting other suicide bombers, killing at least six of the bombers.

The ambush shows “an increased boldness on the part of a rejuvenated Boko Haram,” SBM Intelligence risk analysts said Friday, adding that the extremists’ ranks have been bolstered by an “influx of hardened fighters from the Sahel and Libya.”

A multinational force drove Boko Haram out of towns and villages in northeast Nigeria last year, but attacks and suicide bombings continue.

Boko Haram’s seven-year Islamist uprising has killed more than 20,000 people and driven some 2.6 million from their homes, creating the worst humanitarian crisis on the continent, with millions facing starvation, authorities say.