A suicide bomber blew up his car just outside the police headquarters in the northeast Nigerian city of Maiduguri, killing eight people, a Nigerian Red Cross report said Friday amid warnings that the situation in the city is worsening.

The report said 19 more people were injured in the blast that occurred at about 11 a.m. Friday outside the police headquarters in Maiduguri. It said casualties had been taken to two hospitals.

One hospital official said six bodies were brought to the hospital where he works and that 16 people were hospitalized with injuries from the attack. He spoke on condition of anonymity because he is not allowed to speak to press.

The blast occurred Friday around noon in front of the headquarters' gate after officers prevented the bomber from entering the compound, said Borno State police chief Bala Hassan. Hassan said that only one policeman and two civilians were killed and six civilians were injured. However, officials have downplayed casualty figures in the past.

Hours earlier, a suspected bomber died when an explosive went off prematurely in another part of the city, said military spokesman Col. Victor Ebhaleme.

A radical Islamist sect known as Boko Haram has carried out similar attacks in Maiduguri where residents live in constant fear of the next blast or drive-shooting.

The U.S. Embassy issued a warning late Thursday saying its citizens should not to travel to Maiduguri as diplomats believe "the situation will continue to deteriorate."

Nigeria faces a growing wave of sectarian violence carried out by the sect whose name means "Western education is sacrilege" in the Hausa language of Nigeria's predominantly Muslim north. Boko Haram has been blamed for killing more than 560 people this year alone, according to an Associated Press count. The sect's targets have included churches, police stations and other security buildings, often attacked by suicide car bombers across northern Nigeria.

Maiduguri's police headquarters had been targeted before. Last August, police shot dead a 25-year-old man who attempted to drive a sedan loaded with seven gas cylinders, cans of gasoline and gunpowder into the building. There were no casualties besides the suspected bomber.

Boko Haram, which speaks to journalists through telephone conference calls at times of its choosing, could not be immediately reached for comment Friday afternoon. The sect most recently claimed responsibility for the drive-by killing Tuesday of a retired deputy inspector-general of police and two other officers in Nigeria's largest northern city of Kano.

Many of the sect's casualties have been policemen and soldiers who have responded tit-for-tat, putting residents at further risk.

Nigeria's military says at least 16 people were killed Tuesday following an hours-long gunfight in Maiduguri, the sect's spiritual home.

Authorities told journalists that all those killed were "Boko Haram terrorists." However, a man who lives in the neighborhood said civilians had been hit by stray bullets. The man requested anonymity out of fear of angering the sect or authorities.

Nigeria, a nation of more than 160 million people, is divided between a largely Muslim north and Christian south. Boko Haram attacks have inflamed tensions between the two religions, though many in the faiths live peacefully with each other and intermarry in Africa's most populous nation.