A car loaded with explosives crashed into the main United Nations' building in Nigeria's capital and exploded  Friday, killing 19 people in one of the deadliest assaults on the international body in a decade.

A radical Muslim sect blamed for a series of attacks in the country claimed responsibility for the bombing, a major escalation of its sectarian fight against Nigeria's weak central government.

The brazen assault in a neighbourhood surrounded by heavily fortified diplomatic posts represented the first suicide attack to target foreigners in oil-rich Nigeria, where people already live in fear of the radical Boko Haram sect. The group, which has reported links to al-Qaida, wants to implement a strict version of Shariah law in the nation and is vehemently opposed to Western education and culture.

While police officers and local officials have primarily bore the brunt of Boko Haram's rage, now everyone seems to be a target in a nation often divided by religion and ethnicity.

Car rammed through gates

"It is an attack on the global community," said Viola Onwuliri, a junior Nigerian foreign minister, as she looked at the bomb site.

A sedan loaded with explosives crashed through two gates at the exit of the United Nations compound Friday morning as guards tried in vain to stop it, witnesses told The Associated Press. The suicide bomber inside drove the car through the glass front of the main reception area of the building and detonated the explosives, inflicting the most damage possible, a spokesman for the Nigerian National Emergency Management Agency said.

"I saw scattered bodies," said Michael Ofilaje, a UNICEF worker at the four-story building, which he said shook with the explosion. "Many people are dead."

Nigerian National Emergency Management Agency spokesman Yushau Shuaib confirmed the death toll had risen by one on Saturday to 19.

Nigerian Health Minister Mohammad Ali Pate made a public appeal for blood donations, saying there were at least 60 injured people alone at the nearby National Hospital.

'Terrible act'

The headquarters, known as UN House, had offices for about 400 employees working for 26 UN humanitarian and development agencies.

Authorities worked Friday to account for everyone in the building at the time of the blast.   

UN Secretary-General Ban Ki-moon called the car bombing "an assault on those who devote their lives to helping others."   

"We condemn this terrible act, utterly," Ban told reporters at UN headquarters. "We do not yet have precise casualty figures but they are likely to be considerable. A number of people are dead; many more are wounded."

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An injured man is carried from the UN building in Abuja. (Saharareporters/Associated Press)

   Said Djinnit, the special representative of the UN secretary-general for West Africa, told the AP that he expects the casualties are mostly local staff.

The attack was one of the deadliest attacks on the United Nations in a decade. Seventeen UN civilian staff members were killed along with dozens of others in two terrorist car bombings that targeted UN and other premises in Algiers on Dec. 11, 2007. Friday's bombing also came just days after the UN marked the eighth anniversary of the Aug. 19, 2003 bombing of UN headquarters in Baghdad that killed 15 UN staff including top envoy Sergio Vieira de Mello and seven others.

'Heinous action'

The attack was also condemned by leaders around the world and members of the UN Security Council who individually deplored the targeting of the UN at an open meeting on UN peacekeeping.

U.S. President Barack Obama called the attack "horrific and cowardly" and expressed strong support for the UN's work.

"The people who serve the United Nations do so with a simple purpose: to try to improve the lives of their neighbours and promote the values on which the UN was founded — dignity, freedom, security, and peace," Obama said in a statement. "An attack on Nigerian and international public servants demonstrates the bankruptcy of the ideology that led to this heinous action."

The explosion punched a huge hole in the building, located in the same neighbourhood as the U.S. embassy and other diplomatic posts in Abuja. Workers brought three large cranes to the site within hours of the attack, trying to pull away the concrete and rubble to find survivors.