MAIDUGURI, Nigeria (AP) — Battling multiple bombers strapped with suicide vests, Nigerian troops and civilian self-defence fighters, on Friday, repelled the fiercest Boko Haram extremist attack in months on the key north eastern city of Maiduguri.

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

The United Nations said the attackers targetted refugees in the city that is the birthplace of the Islamic 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 get transportation home, Farhan Haq, deputy spokesman for the UN secretary general, told reporters in New York. “These are not the first attacks affecting the most vulnerable people.”

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-defence 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.

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

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