ABUJA (Reuters) - A car bomb ripped through the United Nations headquarters in the Nigerian capital of Abuja on Friday, killing at least 18 people, in an attack reminiscent of a June blast claimed by a local radical sect. UN Secretary General Ban Ki-moon condemned the attack. We do not yet have precise casualty figures but they are likely to be considerable, he said, adding that the building housed 26 UN humanitarian and development agencies. This was an assault on those who devote their lives to helping others, Ban said in a statement to reporters. We condemn this terrible act, utterly. Security sources and witnesses said the car rammed into the building and blew up, badly damaging parts of an office complex where close to 400 people normally work for UN agencies. Body parts were strewn on the ground as emergency workers, soldiers and police swarmed around the building, cordoned roads and rushed the wounded to hospital. Different people have been taken to different hospitals so were not sure of casualty figures. It is at least 18, said Mike Zuokumor, Abuja police commissioner. No one claimed responsibility for the attack. However, one Abuja-based security source suspected the Nigerian group Boko Haram, whose strikes have been growing in intensity and spreading further afield, or Al-Qaedas North African arm. This is very likely the work of Boko Haram and, or, AQIM (Qaeda in the Islamic Maghreb) and is a serious escalation in the security situation in Nigeria, the security source said. This is the worst thing that could have happened. In Fridays attack the car slammed through security gates of the UN complex, crashed into the basement and exploded, sending vehicles flying and setting the building ablaze. When the car got inside it went straight to the basement and exploded, killing people in reception, right and left, said Abuja resident James John, who witnessed the attack. The entire building, from the ground floor to the topmost, was just fire and smoke. I saw six bodies been carried. I cant believe it. All the people in the basement were killed. Their bodies are littered all over the place. I saw about five dead bodies, said Ocilaje Michael, a UN employee at the complex. The building was blackened from top to bottom. In places, walls were blown away and there were piles of debris from the explosion. Boko Haram, whose name translates from the local northern Hausa language as Western education is sinful, has been behind almost daily bombings and shootings, mostly targeting police in the northeast of Africas most populous nation. The presidency was not available for comment. But security sources and diplomats are increasingly concerned that Boko Haram has links with more organised groups outside Nigeria. These include al Qaeda in the Islamic Maghreb which operates over the border in Niger and has kidnapped foreign workers there. However, it was also suspected of kidnapping a Briton and an Italian in Nigeria earlier this year. In December 2007, a car bombing at the UN building in Algiers killed at least 41 people, among them 17 UN staff. In 2003, 15 staff and seven others were killed by a bomb attack at the UN building in Baghdad. In London, Henry Wilkinson, associate director at Janusian risk consultants, told Reuters the attack suggested Boko Haram had evolved from being a parochial Islamist faction to one that also threatened international targets in Nigeria. This attack will prompt many Western organisations and business to reassess the threat the group poses, he said.