[elombah.com (Nigeria President Goodluck Jonathan, center, speak to journalists, August 27, 2011 after visiting the explosion site at the United Nation's office in Abuja, Nigeria)  Nigeria's president Goodluck Jonathan has visited the United Nations headquarters in the capital, Abuja, the blast site where over 19 people were killed by a car bomb on Friday. the President  again reiterated his commitment

 to tackling Nigeria’s security challenges, vowing to bring terrorism under control.

Touring the shattered offices where a suicide bomber crashed an explosive laden vehicle into the building before detonating the bombs, Jonathan promised to address the threat posed by the radical Islamic sect known as Boko Haram. 

He offered condolences to U.N. Secretary-General Ban Ki-moon for what he called a "dastardly" act.  He said his government is working to bring terrorism "under control," and said it would also work with the U.N. and other world leaders to respond to the attack.

The government has tightened security in Abuja Saturday, with soldiers searching cars at roadblocks and patrolling around the damaged building. 

Authorities say the death toll could still rise as hospitals continue to treat at least 60 people wounded in the blast. About 400 people work at the U.N. compound in Abuja, which houses 26 humanitarian and development agencies.

Witnesses say a vehicle forced its way past two security gates at the sprawling U.N. complex shortly before noon Friday, local time, and exploded inside the compound. 

A man who identified himself as a spokesman for Boko Haram, an extremist Islamic group in Nigeria, says the group is responsible for the bombing. He told a VOA correspondent (Hausa Service) in Nigeria "this is just the beginning."

The spokesman said the bombing was in response to the military's increased presence in northeastern Borno state, where Boko Haram is very active

"Boko Haram is a local group linked up with terrorist activities," Jonathan told journalists gathered at the site. "As a government, we are working on this and we will bring it under control."

Security has been heightened in and around Abuja. Soldiers wearing flak jackets have been seen blocking the main highway heading into the city from Abuja's international airport Saturday morning, checking passing vehicles. 

At the U.N. building, soldiers, police and members of Nigeria's secret police cordoned off the area, looking out at the nearby embassies and buildings, some with broken windows from Friday's blast.

The U.N. had yet to complete a headcount of its staff at the building, which houses about 400 workers, said Agathe Lawson, the acting resident coordinator in Nigeria for the international body. Lawson said her workers had begun to try to find other locations to operate from, and promised the U.N. would continue its work in Nigeria.

"We prepared. Security was in place, but it is never enough," she said as workers salvaged printers and computers from the building's shell. 

Secretary-General Ban told a meeting of the Security Council Friday such "acts of terrorism are unacceptable." He said a U.N. team will travel to the Nigerian capital to assess the situation.  He declined to speculate on who may have carried out the bombing. 

Boko Haram has mostly carried out attacks in Nigeria's northeast, but has also claimed responsibility for several attacks in other regions, including the June bombing of Nigeria's national police headquarters in Abuja. 

The group wants a strict form of Islamic law called sharia to be more widely imposed across Africa's most populous nation.

Boko Haram launched a violent uprising in July 2009 that was crushed by the Nigerian military.  Since then, the group has targeted police, politicians, community leaders and opposition religious figures.