ABUJA, Nigeria - Two top U.N. officials offered conflicting views Sunday on the safety of its Nigeria headquarters after a suicide car bombing there, as the world body paused to mourn the 23 people killed in the attack claimed by a radical Muslim sect.

U.N. security chief Gregory Starr acknowledged that safety features "could have been better" to stop the speeding sedan loaded with explosives. But only hours later, U.N. Deputy Secretary-General Asha-Rose Migiro told journalists that the building had "really, really tight" security.

Migiro earlier laid bouquets of red and white roses near a U.N. flag flying at half staff at the site of Friday's attack, along with Nigeria's foreign minister and the body's acting local representative. She promised the U.N. would continue its work no matter what in Nigeria, an oil-rich country of 150 million people now violently divided by religion and ethnicity.

"We cannot allow ourselves to be intimidated by terrorism," Migiro said.

A suicide bomber rammed through two sets of gates to reach the U.N. building's glass reception hall. There, the bomber detonated explosives powerful enough to bring down parts of the concrete structure and blow out glass windows from other buildings in the quiet neighbourhood filled with diplomatic posts.

While U.N. guards weren't armed, Starr said the Nigerian government provided the compound armed security. It remains unclear how those forces responded, though Nigeria's federal police are more known for asking for bribes and intimidating civilians than protecting the public.

The U.N. also had no specific intelligence or information about Boko Haram, the radical Muslim sect from Nigeria's northeast that claimed responsibility for the attack.

"We had some general threats worldwide and some very mixed, general threat information about the environment" in Nigeria, Starr told The Associated Press. "But no, (we had) no advanced warning."

The U.N. compound had a long driveway that allowed the suicide bomber to pick up speed, Starr acknowledged. The gates were not heavy, as Migiro shook them herself while touring the rubble-strewn grounds. The gates also did not have one-way traffic spikes nor any additional barriers to stop a speeding vehicle.

Despite that, Migiro said the building's security remained strong enough to provide protection while allowing the public access to the U.N.

"If people are plotting, no matter what we're doing, we may continue to be targets," she said.

The death toll for the attack rose Sunday to 23 people killed, said Martin Dawes, a U.N. spokesman attending the trip. Dawes said another 81 people were wounded in the attack. Burial arrangements were still being made for the dead, who included Nigerians, a Kenyan and a citizen of Ivory Coast, Migiro said.

Friday's attack was the first suicide attack targeting foreigners by Boko Haram, a group which has reported links to African terror groups al-Qaida in the Islamic Maghreb and al-Shabab of Somalia. The sect wants to implement a strict version of Shariah law in the nation and is vehemently opposed to Western education and culture.

Boko Haram vowed Saturday to commit future attacks. Hours earlier Saturday, President Goodluck Jonathan promised to bring terrorism in the oil-rich nation "under control."

However, Jonathan's weakened government has so far been unable to stop Boko Haram from carrying out assassinations and bombings at will. The sect is responsible for a rash of killings targeting security officers, local leaders and clerics near Nigeria's volatile northeastern city of Maiduguri over the last year. The group also claimed responsibility for a bombing at national police headquarters that killed at least two people in June.

The group continued its wave of violence Sunday. In Maiduguri, gunmen shot and killed a local politician, the latest assassination to be blamed on the group. In Bauchi, authorities said suspected sect members threw a bomb into the home of a former minister of police in the nation, damaging the house, but not injuring anyone.

Nigeria, a country largely split between a Christian south and Muslim north, remains desperately poor after decades of oil wealth being squandered by its political elite. That poverty has spread resentment throughout the north in recent years, fueling membership in extremist groups like Boko Haram.

Migiro, of Tanzania, also visited Abuja's National Hospital on Sunday, where many of the wounded were treated after the blast. Wearing a surgical mask, she walked among hospital beds in the hospital's intensive care unit. Some of the wounded still had shrapnel in their bodies.

She stopped at one bed, where a U.N. employee named Fred Willis was waiting to go into surgery for a second time.

"Hope you get better," Migiro said, waving her hand over his body in a motion of prayer.

His oxygen mask removed, Willis could only softly reply: "Thank you."